BOTANY VOL. 3 - EVOLUTION AND SYSTEMATICS - 2007

11. SYSTEMATICS AND PHYLOGENY

11.2. Bacteria, Fungi, Plants

Second Division: Streptophyta

In this division, flagella are either absent (Zygnematophyceae) or, if present, are laterally inserted (Klebsormidiophyceae; Charophyceae). During Cell Division, new cell walls (as in the previously discussed Trentepohliophyceae and vascular plants) are formed within phragmoplasts (microtubules are aligned perpendicular to the plane of the future division wall; cf. phycoplast: Chlorophyta, Introduction). The circumscription of this division, as well as its distinction from the previously discussed Chlorophyta, is supported by DNA analysis data.

First Subdivision: Streptophytina (green Algae II)

This subdivision groups together all Streptophyta from unicellular to multicellular algae with a simple Organization. The most advanced forms associated with the aquatic environment achieve a fairly high level of functional differentiation; they develop Tissues (e.g., nodes in Characeae) and protected reproductive Organs.

1. Class: Mesostigmatophyceae

These are monadoid unicellular freshwater organisms (e.g., Mesostigma). Their cell covering appears finely ornamented. It consists of three layers of scales. The scales of the outermost layer (made of organic material) are larger than those of the inner layers and are basket-like. Two flagella of slightly unequal length are subterminally attached. Chlorokybus often forms regularly shaped groups of several (up to 32) Cells. Due to the presence of scales, representatives of this class were formerly assigned to Prasinophyceae (division Chlorophyta); their affiliation with Streptophytina is supported by DNA analysis. It appears that Mesostigmatophyceae is the ancestral group from which the evolution of green land plants originated.

2. Class: Conjugates (Zygnematophyceae, Conjugatae)

Conjugates do not form flagellated stages: they have neither zoospores nor flagellated Gametes. Sexual reproduction occurs via conjugation¹: two naked protoplasts, each representing the entire contents of its cell, fuse to form a zygote. The latter germinates after a dormant period, undergoing Meiosis; the alternation of nuclear phases is zygotic. Consequently, conjugates are obligate haplonts, represented by coccoid or filamentous forms. The filaments are unbranched and easily fragment into individual cells. Each cell contains a nucleus located in its center. Conjugates include approximately 4,000–6,000 species (about 50 genera) living in the benthos and partly in the plankton, almost exclusively in fresh waters.

¹ It should be noted that the term 'conjugation' in biology is rather unfortunately used for very different phenomena (in Ciliates, Bacteria, Chromosomes, and in this case). — Translator's Note.

Mesotaeniaceae — a relatively primitive group. The algae exist either as single cells or form mucilaginous colonies (Fig. 11.103, A; coccoid level of organization). The Cell wall is continuous and smooth.

Fig. 11.103. Streptophytina, Zygnematophyceae; Mesotaeniaceae and Desmidiaceae:

A — Mesotaenium braunii (280x); B — Closterium moniliferum (200x); C — Closterium regulare, transverse section of a cell, the chloroplast has a stellate outline (200x); D, E — Closterium parvulum, conjugation (300x); F — Closterium rostratum, zygote escaping from the wall (200x); G — Closterium sp., zygote division (200x); H — Cosmarium botrytis (280x); J, K — same, division (280x); L — Micrasterias denticulata (125x); M, N — Oocardium stratum, surface view and longitudinal section (320x); O — Desmidium swartzii, part of a cell chain; P — same, transverse section of a cell (350x); dk — degenerated nucleus; g — mucilaginous stalk; k — nucleus; kh — lime sheath; p — pyrenoid; v — vacuole with gypsum crystals

Desmidiaceae² are typically unicellular (coccoid) forms. Their cell walls, which are usually ornamented and often contain iron (hence their yellowish color), consist of two equal halves—semicells—separated from each other by a suture or constriction (isthmus). Each of the two perfectly symmetrical semicells contains a single large, central (not parietal) chloroplast with one or more pyrenoids (see Fig. 2.87; Box 4.1, Fig. C; Fig. 11.103, B, C). The Nucleus is located in the center of The Cell.

² The German name for this group is highly descriptive: Zieralgen (ornamental algae). — Translator's Note.

Vegetative Reproduction occurs by cell division into two, whereby (as in diatoms—see Bacillariophyceae) each daughter cell must regenerate one half of the cell wall (Fig. 11.103, J, K). This process gives rise to new unicellular individuals. However, in some genera, the daughter cells remain attached to each other, forming chains.

During sexual reproduction, two genotypically different cells align with each other (Fig. 11.102, D) and become enclosed in mucilage. The cell wall then splits in the middle, and the protoplasts emerge as naked gametes into a Swelling, soon gelatinizing conjugation tube (bridge) and fuse to form a zygote (E), whose wall is often spiny. Initially, four empty cell wall halves from the two fused cells remain adjacent to the mature hypnozygote. Upon zygote germination, of the four haploid nuclei resulting from meiosis, two degenerate in most Desmidiaceae, so that only two haploid germlings are formed.

Desmidiaceae, which are among the most beautiful algae, are highly diverse in appearance. Their cells, for example, are crescent-shaped (Closterium, Fig. 11.103, B), biscuit-shaped (Cosmarium, H), or star-shaped (Micrasterias, L). Euastrum (see Box 11.7, p. 199) has an apical notch at the ends of the semicells, while Staurastrum (see Box 11.7) has semicells with acute angles. At both ends of Closterium cells, there are vacuoles containing gypsum crystals that exhibit active Brownian motion (B). Some Desmidiaceae secrete mucilage strands through pores in their walls, enabling the cells to move slowly. Individuals of the genus Oocardium, which inhabit lime-rich streams, sit on a mucilaginous stalk incrusted with lime (M, N). Desmids develop predominantly in nutrient-poor waters with low pH, such as peat bogs, where they show great species diversity; Pleurotaenium and Staurastrum also occur in alkaline waters.

The family Zygnemataceae is represented by unbranched filamentous forms. The most well-known genus is Spirogyra (Fig. 11.104, A). Its numerous species are frequently found in spring in standing or slow-flowing waters as free-floating, yellowish-green 'pond scum'. The filaments grow intercalarily by elongation and transverse division of all cells; thus, all cells are equivalent, and filament polarity is absent. The smooth, poreless Cellulose cell walls are covered externally with mucilage, making the filaments slimy to the Touch. During mitosis, the nuclear envelope remains largely intact (closed mitosis). The transverse wall is formed centripetally like an iris Diaphragm and additionally as a cell plate in the phragmoplast. Filaments can fragment at the cross walls into unicellular or multicellular pieces, which serve for vegetative reproduction (see 10.1.3.3).

The nucleus is located in the center of the cell and is suspended by protoplasmic strands within a large vacuole. One or more parietal METABOLISM/14.html">Chloroplasts are clearly visible, always arranged in a left-handed spiral (see Fig. 2.87; 11.104, A, C: c) with pyrenoids (A: p).

Fig. 11.104. Zygnematophyceae: A — H — Spirogyra: A — S. jugalis, cell (250x), B — S. quinina, anisogamous conjugation (240x), C — H — S. longata; C — portion of chloroplast near the cell wall (750x), D — H — young and old zygotes, D — two sexual nuclei before conjugation, E — after fusion, F — division of the zygote nucleus into 4 haploid nuclei, G — three small nuclei degenerating (D — G — 250x), H — uninucleate germling (180x); J — L — Mougeotia: J, K — M. scalaris, chloroplast facing the viewer with its broad side ('face view') and narrow side ('profile view') (600x), L — M. calospora, isogamous conjugation (450x); c, c1, c2 — chloroplast(s); k — nucleus; p — pyrenoid; s — starch; w — cell wall; z — zygote; zw — zygote wall

During sexual reproduction, two filaments, which are usually morphologically indistinguishable, lie parallel to each other. Papillae protrude from the cells along the line of contact, pushing the filaments slightly apart again and forming a ladder-like Structure (scalariform conjugation; see Fig. 11.104, B). Due to the lysis of the cell wall at the point of contact, the papillae fuse to form a conjugation tube between the corresponding cells ("gametangia"). Any cell of the filament can become a "gametangium". Sex Determination is modificational (♂ and ♀ filaments). The protoplast of the ♂ cell, acting as a naked "migrating gamete", passes into the adjacent ♀ cell and fuses with its protoplast ("stationary gamete"). The resulting zygote decreases in volume by losing Water and transforms into a hypnozygote (Fig. 11.104, B: z), which becomes surrounded by a thick, multilayered brown wall, contains abundant starch and oil, and in this state survives unfavorable conditions. The chloroplast(s) of the ♂ "gamete" degenerate. Upon zygote germination, which involves meiosis, 3 nuclei (F, G) degenerate, so that only a single haploid germling emerges, which elongates and undergoes cell divisions to form a new filament (H).

Some species of Spirogyra are monoecious. In these, the protoplasts of adjacent Cells of the same filament fuse through lateral conjugation tubes (lateral conjugation).

Zygnema and Mougeotia differ in The structure of their chloroplasts. In Zygnema, each cell contains two stellate chloroplasts, while in Mougeotia (Fig. 11.104, J, K), There is a single chloroplast in the form of a flat axial plate that responds to light (cf. 8.2.2). In both genera, there are species in which the zygote is formed within the conjugation tube (L); this process resembles that in Representatives of the previous order.

Zygnematophyceae is a group that clearly differs from other green algae in its mode of reproduction and Cell Structure, from which it apparently diverged early in evolution, completely losing flagellated stages.

3. Class: Klebsormidiophyceae (Coleochaetophyceae)

The cell wall of the filamentous (unbranched and branched) representatives of this class contains cellulose (fibrillar arrangement). Flagellated reproductive cells are covered with diamond-shaped organic scales; in this respect, they resemble the cells of Mesostigmatophyceae. Species of this class occur in fresh waters and in damp terrestrial habitats. In the order Coleochaetales, species are represented by branched filaments. Their thallus is differentiated into a sole and erect filaments (heterotrichous structure; Fig. 11.105; a similar thallus differentiation is found in Trentepohliophyceae and Chaetophorales of the Chlorophyceae).

Coleochaete exhibits a high level of development among the Chlorophyta (presence of a discoid sole — Fig. 11.105, A; uniquely differentiated hairs; oogamous reproduction). The bottle-shaped oogonium has a colorless neck (C), which opens at the apex to allow The entry of colorless, biflagellate spermatozoids. After Fertilization, the spherical zygote increases in size, while filaments grow from its supporting cell and neighboring cells, so that eventually the zygote is enclosed in a single-layered plectenchyma, forming a "fruiting body" (E). Upon germination of this resting organ, meiozoospores do not form immediately; instead, after meiosis, a haploid body of 16 to 32 cells is formed inside the zygote, with a single haploid zoospore developing in each cell.

Klebsormidiophyceae are named after the genus Klebsormidium, whose species have a coccoid structure or are represented by unbranched filaments.

Fig. 11.105. Streptophytina, Klebsormidiophyceae: A — Coleochaete scutata, sole (80x); B — Aphanochaete repens, development of a sheathed bristle (250x); C — E — Coleochaete pulvinata, C — oogonium shortly before opening; D — the same, fertilized; E — zygote transforming into a "fruit" due to the overgrowth of filaments (500x); ek — egg Cell Nucleus; sk — spermatozoid nucleus

Among the green algae, Coleochaetophyceae, together with the Charophyceae (not yet discussed), are the closest relatives of green land plants. This class of algae shares common features with bryophytes and pteridophytes, such as laterally inserted flagella, a tendency toward tissue formation, Protection of the zygote (the onset of embryo formation), a phragmoplast, and the same type of cellulose. The "fruiting bodies" of Coleochaete are protected against desiccation and microbial decay by sporopollenin and Lignin-like compounds.

4. Class: Charophyceae (stoneworts)

The Charophyceae are highly developed green algae with thalli in which tissue-like and filamentous regions strictly alternate in sequence

(nodes and internodes, respectively). The reproductive organs achieve a highly specific complexity absent in all previous groups. Represented by only a few genera, the Charophyceae form "underwater meadows" in ponds and streams. About 300 species are known. They inhabit fresh and brackish waters; freshwater species often develop particularly abundantly in water bodies with high pH values (pH 7 and above; hard water). Characeae is the only family of the class with extant representatives.

The cell walls are often incrusted with lime; some Characeae are among the most important formers of calcareous tufa. They do not tolerate high concentrations of phosphates from water pollution.

Structure. The main and lateral axes exhibit apical growth, growing by means of a single apical cell (see Fig. 5.9, B). It cuts off, in alternating succession, narrower cells (future nodes) and more elongated cells (future internodes) in the basal direction; the latter do not divide further and elongate, undergoing vacuolation, up to several centimeters.

Thus, the stoneworts are characterized by a regular division of the thallus, which can reach several decimeters in length, into nodes (nodi) and internodes (internodia).

The cells of the nodes retain their ability to divide and develop into multicellular nodal discs, from which whorls of jointed lateral axes of various orders arise. In addition, short, subulate "stipulode" cells and cortical cells are formed. Cortical cells (characteristic of the genus Chara and absent in species of the genus Nitella, etc.) form a sheath of filamentous cells closely appressed to the internodes.

Lateral branches show a similar subdivision to the main axis. They are ecorticate, simple, or bear short lateral Branches of the second order at their nodes, with a similar subdivision into nodes and internodes.

In each whorl, a long "SHOOT" resembling the main axis can arise from the "axil" of the short "shoots" (see Fig. 5.9).

At their bases, the plants are anchored to loose substrate (mud, sand) by means of colorless, branched, filamentous rhizoids arising from the nodes. Some Characeae form bulbils tightly packed with starch from the lower PARTS OF THE axes, which serve as overwintering organs.

Young cells are uninucleate immediately after cell division. In the long internodal cells, the nucleus grows endomitotically and fragments into numerous nuclear portions, so that these cells become multinucleate. The Cytoplasm is usually in active streaming (cytoplasmic streaming, see 8.2.2). Numerous chloroplasts are located in the parietal cytoplasm of the cells.

The solid part of the cell wall consists of cellulose, which in its ultrastructure is similar to the cellulose of higher plants. New transverse cell walls arise in phragmoplasts.

Reproduction. The Charophyceae are all oogamous haplonts with a zygotic alternation of nuclear phases. The vertically oriented oogonia of Chara are surrounded by spirally twisted cortical filaments. Male gametes arise in spherical receptacles of complex structure (spermogonia of Chara). The biflagellate spermatozoids are corkscrew-shaped, whereas in all other green algae they are radially symmetrical. The spherical spermogonia, which are colored yellow-red by carotenoids when mature, and the ovoid green oogonia (both visible to the naked eye) are formed at the nodes of the lateral axes.

Fig. 11.106. Streptophytina, Charophyceae: A — LATERAL VIEW OF a portion of the thallus with a spermogonium (s) and an oogonium (o), cortical filaments, and a corona (c) (50x); B — manubrium with a capitulum and spermatogenous filaments; C — cells of a spermatogenous filament, each containing one spermatozoid; D — spermatozoid (540x); E — longitudinal section through a young spermogonium; g — flagella; gz — manubrium; k — spirally coiled long nucleus; kz — capitulum; p — cytoplasm; w — wall

Box 11.7. Occurrence and lifestyle of algae

The vast majority of algae are photoautotrophs. They are contrasted with mixotrophic and heterotrophic forms. Mixotrophy allows photosynthetic organisms to additionally absorb organic matter from the nutrient-rich environment. Heterotrophic algae have lost their Photosynthetic Pigments and feed on preformed organic substances; 'phagotrophic' representatives of this group 'ingest' solid food particles that enter digestive vacuoles. While phototrophic algae are typical plants, their pigment-free phagotrophic counterparts exhibit an animal-like lifestyle. Among flagellate forms, closely related species with autotrophic (plant-like) and phagotrophic (animal-like) organization can coexist. Thus, the boundaries between plants and animals are still blurred at this relatively low evolutionary level.

Although prokaryotic and eukaryotic algae occur in almost all biotopes, most species inhabit water, where they either float freely in the water Column as 'plankton' or attach to rocks, sand, and other substrates as 'benthos'. Due to differences in salinity, There are two types of aquatic habitats: marine and fresh waters.

Marine algae

Marine phytoplankton is represented primarily by diatoms and dinophytes (dinoflagellates), as well as tiny haptophytes (Coccolithophorales) and golden algae (silicoflagellates). Representatives of the latter two groups are not retained by the mesh of plankton nets and can only be collected by centrifugation ('nanoplankton').

The highest plankton density (up to 100,000 cells per liter of water) is observed in the well-lit water layer. One liter of surface water in the Atlantic near the Faroe Islands was found to contain: 32,000 dinophyte cells, 1,600 diatoms, and 54,000 coccolithophorids. Below a depth of 100 m, the number of these planktonic forms drops sharply. However, even at great depths (4,000 — 5,000 m), Coccolithophoraceae and 'olive-green cells' (whose systematic position is still unclear) are still encountered. Furthermore, the highest plankton density occurs in colder seas and in areas of cold ocean currents; this is because these waters are richer in nitrogen compounds and phosphates. These substances are consumed in the water layers closer to the surface and accumulate in deeper layers due to the sinking of dead cells. In cold regions, due to both winter and nocturnal cooling of the sea surface, the water mixes better than in the tropics, leading to more intensive plankton development. An Abundance of plankton is also observed where cold deep waters, saturated with nitrogen compounds and phosphates, rise to the surface due to currents.

The suspension of planktonic organisms in water would lead to their more or less slow sinking if it were not regulated by specific gravity and frictional drag, as well as the active movement of flagella. This explains many features of planktonic algae: the presence (Synthesis and Breakdown) of oil as a storage substance, The Development of appendages and projecting cell walls (see Fig. 11.70), and the grouping of many cells into chains (see Fig. 11.76). It has been noted that in warm waters (where viscosity is lower), the appendages serving for suspension are larger than in cold ones. The mineral skeletons of planktonic algae settle to the sea floor. Since calcium carbonate dissolves at depths greater than 4,000 — 5,000 m, at great depths we find only the skeletons of diatoms, silicoflagellates, and, among animals, radiolarians. At shallower depths (2,000 — 5,000 m), calcium carbonate deposition also occurs (Coccolithophoraceae, and among animals, globigerinae, etc.). Over 1,000 years, a layer only 1.5 cm thick is deposited. The phytobenthos in the seas consists (excluding the seagrass Zosteraceae) exclusively of algae, predominantly brown and red. Most often, they attach to a hard substrate (rock) using holdfasts or appendages (see Figs. 11.83, 11.85). Mobile substrates (mud, sand) are colonized by species of only a few genera, such as Caulerpa (see Fig. 11.91, A). Benthic algae are found from the splash zone to depths where Photosynthesis is still possible (180 m).

In tropical seas, algal vegetation does not reach such luxuriance as in the seas of temperate and cold zones (cf. the reasons given for planktonic forms). Brown algae are represented to a much lesser extent, whereas red algae, by contrast, are quite widespread, as are some thermophilic green algae: Caulerpaceae, Dasycladaceae, Codiaceae, and Valoniaceae. Coral reef vegetation is also rich, with algae (Halimeda, see Fig. 11.91, B; Dasycladaceae, see Fig. 11.92, B; Lithothamnion) playing a greater role in calcium carbonate formation than the corals themselves. A unique phenomenon is the 'Sargasso Sea', where the brown alga Sargassum (see Fig. 11.85, A), floating on the water surface, forms abundant mats (plants drifted together reach up to 5 t of phytomass per square nautical mile).

In warm-temperate seas, such as the Mediterranean, the benthos consists mainly of red and relatively small brown algae. The aforementioned Bryopsidophyceae and Dasycladophyceae are represented by a few species. Lithothamnion species are widely represented. Since light intensity depends on the season, the main period of algal development near the water surface is spring, at depth it is summer, and in autumn algae generally develop less.

In cold-temperate seas, such as the North Sea, brown algae clearly dominate, both in size and biomass. The season significantly affects many species. For example, Desmarestia loses its assimilating hairs in autumn, and the red alga Delesseria loses the delicate flat parts of its thallus, so that only the 'midribs' overwinter.

Large kelps (see Fig. 11.83) shed and renew their phylloids annually. Fig. 11.107 shows, using the rocky coast of the English Channel as an example, a well-defined vertical zonation of algal vegetation depending on the tidal level. Species of the upper zones (Bangia, Porphyra, Fucus) can withstand temperatures down to -20 °C, whereas inhabitants of deeper zones that are never exposed to desiccation (Laminaria, Delesseria) die off at just a few degrees below zero. Cold seas have a species-poor algal composition, yet it is here that the thalli of brown algae reach their largest sizes: Examples include Macrocystis (see Fig. 11.83, E), Lessonia (D), and Nereocystis (C) — all belonging to the Laminariales, as well as Durvillaea from the Fucales. They are virtually equal in size to large terrestrial plants.

Fig. 11.107. Vegetation profile on the coast of the English Channel: Chlorophyta: Prasiola, Urospora, Enteromorpha; Rhodophyta: Bangia, Porphyra, Rhodymenia, calcareous crusts (e.g., Lithothamnion); Phaeophyceae: Pelvetia, Fucus, Ascophyllum, Alaria, Laminaria, Halidrys, Cystoseira; Lichens: Verrucaria

The distribution of marine benthic algae depends on pollution and nutrient availability. For example, Ulva grows in very nutrient-rich water, Padina in water with a moderate nutrient content, and Sargassum and Fucus in waters with low organic content. Brackish waters occupy an intermediate position between marine and fresh waters. Here, fresh and salt water mix due to regular tides or surf. Estuaries of flowing waters, with their specific planktonic and benthic algae (e.g., Characeae), also belong to this type of habitat.

Freshwater algae

In fresh water, the species composition of phytoplankton depends largely on nutrient availability; in nutrient-rich (eutrophic) water bodies, they also absorb organic substances (mixotrophy). In temperate regions, seasonal variations in water Temperature, light intensity, pH, and other parameters significantly affect plankton composition. In fresh water, the amplitude of temperature fluctuations is much greater than in the sea. Their range extends from the melting temperature (about 0 °C) of glaciers and polar ice — habitats of certain, often red-colored Chlamydomonas, Chlorococcales, and Mesotaeniaceae that make up the 'cryoplankton' — to the temperatures of hot springs, where some diatoms (up to 50 °C) and prokaryotic blue-green algae (up to 75 °C) can still develop. In the benthos of fresh waters, flowering plants clearly dominate in terms of biomass and species diversity, and only under certain conditions do algae (e.g., Characeae) dominate.

The neuston (the community of the water surface) is represented primarily by unicellular algae, such as Euglena species and Chromulina rosanoffii. For the latter species, which imparts a golden sheen to the water surface, densities of up to 40,000 cells per 1 mm² have been recorded. A distinction should be made between the epineuston, which lives above the surface film, and the hyponeuston, which hangs from it into the water.

Algae and water quality

With increasing eutrophication of a water body, biomass production increases significantly, and with it, oxygen consumption: rotting sludge is deposited on the bottom (instead of the mineral sediments of oligotrophic lakes). Nutrient-poor (oligotrophic) water bodies are in severe decline due to artificial fertilization of gardens and fields, as well as general water pollution. The presence of indicator species (planktonic and benthic) can be used to assess the level of pollution and, accordingly, water quality (the saprobity level, designated by numbers from I to IV). Along with eukaryotic algae, prokaryotes (blue-green algae, bacteria), Fungi, and higher plants are also used as indicators for this purpose.

The most severe pollution is designated as IV (polysaprobic zone). Here, due to oxygen deficiency, putrefaction processes predominate. Oxygen depletion is extremely high. Under extreme living conditions in the polysaprobic zone, there is massive development of bacteria, including Beggiatoa, as well as prokaryotic blue-green algae of the genera Spirulina and Anabaena. However, eukaryotic algae and aquatic higher plants are almost completely absent; the only exceptions are Euglena and Carteria species. Along with these few green-colored algae, the colorless heterotrophic Polytoma is also found. Even with heavy pollution, for example, from untreated wastewater, a certain degree of self-purification of watercourses can occur.

In heavily polluted Class III waters (α-mesosaprobic zone), oxidative processes are vigorously initiated. A high abundance of various bacteria is also characteristic of this state, but at the same time, a massive development of algae — blue-green, as well as diatoms and green algae — is observed; some higher plants also begin to develop well. The oxygen content can be significant and exceed the saturation value during the day, but it drops sharply at night. Among prokaryotic algae, various Oscillatoria species are found here (whereas in Class IV waters, only O. putida and O. chlorina occur) and Phormidium; among diatoms, Stephanodiscus; among conjugates, Closterium leibleinii and Cosmarium botrytis; among other green algae, Chlamydomonas and Gonium. Sewage fungi of the genera Leptomitus and Fusarium are also characteristic.

Moderately polluted Class II waters (β-mesosaprobic) are characterized by even more successful oxidative processes; accordingly, oxygen depletion is relatively minor. In this zone, the Number of viable bacterial cells becomes even lower. Conversely, a high diversity of diatoms and green algae is observed. Blue-green algae are represented by Anabaena flos-aquae, Nostoc, and some Oscillatoria species. Among diatoms, various species of the genera Melosira, Asterionella, etc., are found, and among golden algae, Synura. Among green algae, Pediastrum, Scenedesmus, Chaetophora, and Oedogonium can be mentioned. Among desmids, various Closterium species are particularly common.

Almost unpolluted waters are classified as Class I quality (oligosaprobic). In this zone, the water, except for temporary 'blooms', is clear and rich in oxygen. If this area is located downstream from a polluted section of a river, the organic matter here is already decomposed, the intensity of the very rapid decomposition processes decreases, and the oxidation processes are complete. The number of viable bacterial cells drops to minimum values. Among blue-green algae, representatives of the genus Hapalosiphon are characteristic, for example. Diatoms are represented by Surirella and Meridion species, green algae by Ulothrix, Cladophora (glomerata), Spirogyra (fluviatilis) species, and A wide variety of desmid species (from the genera Closterium, Staurastrum, Euastrum, Micrasterias), and yellow-green algae by Vaucheria species. The presence of freshwater algae such as Lemanea annulata and Batrachospermum moniliforme is also typical.

Aerophilic algae, symbionts, and rock-forming organisms

Only a few algae live as aerophilic organisms out of water, primarily on the shaded side of rocks and tree trunks (e.g., algae such as *Pleurococcus* and *Trentepohlia*, see Fig. 11.93, A, C; "ink streaks" of cyanobacteria). They are most common in the humid tropics, where they also colonize leaves. Suitable calcareous substrates near the surface (to a depth of a few millimeters) are often penetrated by algae. Even more widespread, but still little studied, are soil algae. Besides cyanobacteria, the "edaphon"—the community of living soil organisms—includes various green, yellow-green, and diatom algae. Up to 100,000 algal cells have been found in 1 g of soil from the uppermost layer. The green alga *Fritschiella* has adapted to a terrestrial lifestyle in a unique way (see Fig. 11.99, C).

Various symbiotic algae play an important role in nature. They are also often of great importance as rock-forming organisms (e.g., Dasycladophyceae).

Spermogonia (Fig. 11.106, A: s, E) arise from a mother cell that initially divides into 8 cells—octants. Each octant then divides by periclinal (tangential) walls into 3 cells (E). This results in a total of 24 cells, which divide the spherical spermogonium as follows: 8 flat outer shield cells (shields), which acquire a fan-like ornamentation due to developing incomplete radial septa; 8 middle cells (manubria), whi-

ch extend from the centers of the shields and elongate; 8 inner cells (primary capitular cells), which ultimately assume a rounded shape. Be-

cause the 8 shields grow more intensively in width than in thickness, a cavity is formed inside the sphere. Directed toward its center from the center of each shield are the manu-

brial cells, each bearing a single primary capitular cell. The primary capitula give rise to 3–6 secondary capitula, from which grow 3–5 long, unbranched spermatogenous filaments consisting of a single row of cells that fill the cavity (Fig. 11.106, B, C). In each of the disk-shaped cells, a single spirally coiled spermatozoid (D) with 2 flagella and an eyespot, but without Plastids, is formed.

The oogonium (see Fig. 11.106, A: o) contains a single egg cell, densely packed with oil droplets and starch grains. This oogonium projects forward and is later tightly enveloped by 5 cortical filaments twisted in a left-handed spiral. Their tips cut off (by forming a transverse septum) the crown cells (A: c), between which the spermatozoid penetrates. After fertilization, the zygote is surrounded by a thick, colorless wall. In addition, the inner walls of the cortical filaments thicken, turn brown, and are often encrusted with lime, while the outer soft walls disappear shortly after the release of the "oospore" (resting organ). Upon germination of the zygote, meiosis occurs; of the 4 haploid nuclei, 3 degenerate, so that only a single germling arises.

The peculiar structure of the thallus, as well as the spermogonia and oogonia with their unique protective envelopes that have no analogues among other plants, and the spirally coiled spermatozoids, indicate a clearly isolated position of the Charophyceae in The system of living organisms. All these features testify to the uniqueness of the charophytes; however, in terms of pigment composition and storage substances, they are similar to other Chlorophyta and Streptophyta.

Fossil charophytes (especially in the form of their zygotes) have been known since the Silurian; of the 6 families that previously existed on Earth, only one survives today.

Overview of Streptophytina. Most of the living terrestrial green plants originated from the ancestral streptophytes. From them arose the green algae already discussed (II; Streptophytina) and the bryophytes (see Bryophytina) and vascular plants (see Pteridophytina and beyond) not yet considered. The evolutionary relationship of these groups is confirmed by shared features such as: chloroplast ultrastructure; pigment composition (chlorophylls a and b!); arrangement and structure of pyrenoids; starch as a storage nutrient; isokont motile stages with laterally inserted flagella; cellulose as a cell wall building material, specifically in an ordered crystalline form and as microfibrils. Transverse cell walls arise in phragmoplasts. In green algae (II), a kind of "fructification" already occurs, so that fertilization induces the development of enveloping filaments that grow around the oogonium (Coleochaete). In Charophyceae, the envelope of the oogonium is formed before fertilization. In some representatives (e.g., Chara), chloroplasts are completely reduced in ♂ gametes. In Zygnematophyceae, flagellated cells are absent. In some species, sporopollenin and lignin-like compounds occur as protective substances (Coleochaete).

However, bryophytes and vascular plants, despite sharing many features with green algae (II), have undergone significant further development of their reproductive and vegetative structures, indicating clear evolutionary progress (adaptation to terrestrial life!).

Second subdivision: bryophytes (Bryophytina)¹

¹ The authors follow a Classification system for this group that is far from generally accepted. — Editor's note.

For the most part, bryophytes have already developed highly organized tissue thalli²; in this they differ from the green algae of the previous division, which are still adapted to aquatic life.

² Most mosses have a shoot-like organization. — Editor's note.

Box 11.8. Embryophytes

Embryophytes include plants whose sporophyte begins its existence as a resting multicellular embryo that is nourished by the maternal plant and often remains in a dormant state for a long time (as in angiosperms). Admittedly, the presence of an embryo in a rudimentary form is already observed in some aquatic algae (Coleochaete) with resting zygotes protected by the gametophyte.

Typical embryophytes (bryophytes and vascular plants) are primarily terrestrial plants with increasingly complex vegetative organs that serve for anchorage in the soil, absorption of water and nutrient salts, and photosynthesis (see Fig. 4.8; 4.1.2 and 5.3.4). From an initially thalloid vegetative body, different organs developed during ADAPTATION TO A terrestrial lifestyle, in connection with increasing size and division of labor: in the gametophytes of higher bryophytes, the cauloid, phylloid, and rhizoid (see 5.3.4); in the sporophyte of vascular plants, the stem, leaf, and ROOT (see 4.1.2).

Reproduction occurs through a heterophasic and heteromorphic Morphology/12.html">ALTERNATION OF GENERATIONS, in which The life cycle is dominated either by the gametophyte (bryophytes) or the sporophyte (ferns, seed plants). After fertilization, the zygote develops into a multicellular embryo nourished by the maternal plant. The gametangia—here called antheridia (♂) and archegonia (♀)—have an envelope (wall) of sterile cells that protects the gametocytes. Unlike the sporangia of fungi and algae, the sporangia of embryophytes also possess a similar envelope of sterile cells. Such protective structures are completely absent in fungi and are only rarely found in the gametangia of algae.

The meiosporangia of fungi are often protected by a mesh of hyphae in fruiting bodies, but they lack an envelope made of a layer of sterile cells. In algae of the genera Coleochaete and Chara, the oogonium is covered (postgenitally) by outgrowing filaments (see Figs. 11.105, 11.106, E). The wall of the spermogonium of Chara can be compared primarily with the congenital multicellular walls of embryophyte antheridia.

The vegetative body is composed of various tissues that are highly differentiated and perform different Functions. Transpiration is reduced by a cuticle and is usually regulated by Stomata. Water and nutrient transport sometimes occurs through simple conducting strands (bryophytes) or through increasingly structurally complex vascular bundles (ferns, seed plants). Plastids contain chlorophylls a and b, as well as carotenoids. The assimilation product is starch formed in the chloroplasts. Cell walls consist of cellulose¹.

¹ The fibrillar framework of embryophyte cell walls, which is embedded in an "amorphous" matrix of Polysaccharides, consists of cellulose. — Editor's note.

Embryophytes are subdivided into bryophytes (Bryophytina), pteridophytes (Pteridophytina), and seed plants (Spermatophyta). In seed plants, the antheridia and archegonia are highly reduced, so that they are barely recognizable as such². Seed plants are therefore no longer classified as archegoniates in the narrow sense (= bryophytes and pteridophytes). The collective term cormophytes (or also Cormobionta; in contrast to Protobionta with a simpler organization, such as algae and fungi) derives from THE CONCEPT OF a "cormus"—a vegetative body differentiated into stem, leaves, and roots (see Fig. 4.8)—and includes bryophytes with differently differentiated sporophytes, since they can in any case be derived from telomes.

² In all modern gymnosperms and Ephedra, the archegonia are easily distinguishable. — Editor's note.

Thus, as an exception, the sporogonia of bryophytes can branch dichotomously under abnormal development. The conducting systems of bryophytes, if present at all, are quite simply structured. However, they exhibit functional and even certain structural similarities to the conducting elements of vascular plants. All embryophytes are closely related to one another, so they can be regarded as a monophyletic group whose representatives evolved in different directions and reached different Levels of organization.

The Life Cycle of bryophytes is based on a distinct heteromorphic alternation of generations (Fig. 11.108, D), in which the green photoautotrophic gametophyte alternates with the sporophyte. The gametophyte is represented either by a morphologically poorly differentiated lobed thallus with rhizoids underneath (thalloid bryophytes), sometimes with high tissue differentiation (for example, into assimilatory and storage tissues), or by stems ranging from prostrate to erect, covered with leaves and rhizoids (leafy bryophytes). The leaves, except for the midrib¹, are usually single-layered (the leaves of ferns and seed plants are multi-layered). Leafy bryophytes somewhat resemble vascular plants in appearance, but differ from the latter, in particular, in that the gametophyte, rather than the sporophyte, has reached the highest morphological and anatomical level of differentiation. In addition, bryophytes lack vascular bundles, and in most cases, conducting tissues. Rhizoids in bryophytes are unicellular or multicellular filamentous structures that are by no means comparable to the highly differentiated roots of vascular plants (rather, they can be compared to root hairs). The cuticle of bryophytes is usually very delicate, and they typically dry out quickly in the absence of water (poikilohydric plants, see 6.10.3.6). Almost all gametophytes lack stomata (exception: hornworts), but respiratory pores very rarely serve for gas exchange (Marchantiales, see Fig. 11.100, A).

¹ In Jungermanniales, there is no midrib, and the leaf is entirely single-layered. — Editor's note.

Fig. 11.108. Bryophytina: A — sperm reaches the egg cell; B — penetration of the sperm into the egg cell; C — sperm in the Nucleus of the egg cell, the remnant of its cytoplasm remains in the cytoplasm of the egg cell; D — development of a dioecious leafy moss (spore, protonema, gametophyte — G, fertilization, sporophyte — S, reduction division, spores). Light lines — haploid phase; dark lines — diploid phase; g — flagella, k — cell nucleus, p — plastids, R! — reduction division

The archegonia of bryophytes (see Fig. 11.111, J) are flask-shaped organs, the parts of which — the venter and the neck — usually have a single-layered wall. The venter encloses a large central cell, which before maturation divides into an egg cell and a ventral canal cell located at the Base of the neck. In the neck, it is adjoined by neck canal cells; there are always several such cells in bryophytes, arranged in a single row (see Fig. 11.111, J).

Antheridia (see Fig. 11.111, E) are spherical or club-shaped structures on a short stalk. The spermatogenous cells developing within them, surrounded by the antheridial wall, each divide into 2 spermatids, which separate from each other and each transform into 1 sperm cell.

Sperm cells are always short, somewhat spirally coiled, thread-like, with the cell nucleus occupying most of their volume. Near the anterior end, they bear 2 long, smooth flagella (F) directed backward at an acute angle from the point of attachment, and in some representatives, there is also a very small plastid in the cytoplasm (see Fig. 11.108, A: p). Egg cells may also contain a few very small chloroplasts.

Fertilization of the egg cell, even in terrestrial forms, can only occur in the Presence of water (rain, dew). For this, the archegonium opens at the apex, the canal cells disintegrate into mucilage and secrete certain substances that chemotactically attract the sperm cells (see 8.2.1.1). The fertilized egg cell gives rise to a diploid embryo (see Fig. 11.111, K), which always develops into a sporophyte without a resting period.

The diploid sporophyte generation, therefore, always develops on the dominant haploid gametophyte and remains attached to it throughout its life. Isolated sporophytes cannot develop fully, despite possessing chlorophyll. The growth of the sporophyte is, consequently, largely supported by the gametophyte. The nourishment of one generation by another, which is common in plants (for example, in red algae), is called "gonotrophy" (nourishment by the parent). Transport of substances into the sporophyte decreases or stops entirely when it reaches about 2/3 of its final size. Stomata, which first appear in the evolution of land plants in bryophytes, are formed almost exclusively on sporophytes (see Fig. 11.127, G). The sporophyte embeds its basal part (the haustorium, also called the FOOT, see Fig. 11.127, D; 11.120, C) into the deeper tissue of the gametophyte, but grows mainly toward the apex of the archegonium, forming a spherical or oval sporangium (capsule, see Fig. 11.111, L, 11.123, M) on a short or more or less long seta. The entire sporophyte is called a sporogonium.

In the inner tissue of the capsule — the archesporium — As a result of two successive meiotic Divisions of the spore mother cells, meiospores arise in groups of four (tetrads), which separate from each other and round off upon maturation. Dispersal of meiospores is airborne. The wall of the spores consists of an inner delicate endospore and an outer resistant exospore; the latter ruptures when the spore germinates. Spores germinate into gametophytes, forming a filamentous or thalloid protonema (see Fig. 11.123, A, B, C; 11.120, D; 11.108, D), which soon develops into the green moss plant¹.

¹ This is the gametophore. — Translator's note.

Along with reproduction by spores, bryophytes very frequently exhibit vegetative reproduction, for example, by means of gemmae (see Fig. 11.110, A; 11.114, C, G; see 10.1.3.3), which can arise in various ways on gametophytes: on stems, leaves, or the protonema. They detach and grow into a new plant.

Tissue growth occurs by means of a 2-, 3-, or many-sided apical cell (see 5.3.4, Fig. 5.13), or less frequently, by means of a meristem (for example, Riella, Riccia, and Anthoceros).

Lignin is absent in bryophytes; only extremely rarely are lignin-like compounds found (as is already the case in some green algae — Coleochaete).

Systematics. Bryophytes include approximately 24,000 species, which can be subdivided into four evolutionarily distant groups: Marchantiopsida, Jungermanniopsida, Bryopsida, and Anthocerotopsida. Bryopsida are also called mosses (always leafy; leaves with specific characteristics), while representatives of all other classes are grouped under the name liverworts. However, representatives of Anthocerotopsida are apparently evolutionarily closer to other land plants than to any other group of bryophytes, so they are presented here in the Appendix to the mosses.

1. Class: Marchantiopsida (= Hepaticae p.p., thalloid liverworts)

The gametophyte of Marchantiopsida is a flattened, usually more or less dichotomously branched, highly differentiated tissue thallus. On the underside, it typically bears smooth and so-called pegged (or tuberculate) rhizoids, which have inward-projecting wall thickenings. Typically, antheridia and archegonia are elevated on specialized branches (gametangiophores, or receptacles). The cells contain one or several "oil bodies" surrounded by a single membrane (consisting of coalesced terpene droplets), which do not exist in this form in any other plants (see Fig. 11.110, G: ok). The sporophyte remains completely enclosed for a long time by the expanding wall of the archegonium — the embryotheca, which it ruptures at the apex only shortly before maturation. In the maturing sporogonium, each cell of the archesporium divides into a spore mother cell and an elater, which are thus synchronously arising sister cells.

After meiosis, 4 spores arise from each spore mother cell. In contrast to Anthocerotopsida, the 4:1 ratio of haploid spores (4) to sterile diploid elaters (1) can shift in favor of the number of spores (for example, 8:1, 128:1). The spore mother cells and elater mother cells are separated from each other by longitudinal walls, i.e., walls parallel to the longitudinal axis of the sporogonium.

The walls of elaters most often have spiral thickenings (in Anthocerotopsida they are usually smooth). Convergent evolution of elaters in Anthocerotopsida, Marchantiopsida, and Jungermanniopsida¹ cannot be ruled out. Elaters belong to structures that facilitate spore dispersal (such as the capillitium — see, for example, Trichia; gleba fibers — see, for example, Lycoperdon; elaters/haptera — see, for example, Equisetum), which should be regarded as analogous structures.

¹ The elaters of Anthocerotopsida are so different from those of liverworts that their convergent origin has long been beyond doubt. — Editor's note.

The antheridium (see Fig. 11.111, E) arises from a single epidermal cell¹, which divides by vertical, mutually perpendicular walls into 4 cells, after which, in the quadrants of this tower-like structure, division by tangential walls separates the peripheral jacket cells from the inner cells that give rise to the spermatogenous tissue².

¹ More precisely, the protoderm. — Editor's note.

² This is an inaccurate description of antheridium development in this group. — Editor's note.

During the development of archegonia (see Fig. 11.111, J), a single epidermal cell³ protruding above the neighboring cells divides by a periclinal wall into a lower cell, which gives rise to the stalk, and an upper cell, the archegonial initial. Three anticlinal walls divide it into a central axial cell and three jacket cells forming tangential sectors. In a cross-section through a young archegonial initial, all 4 cells can be seen; in a longitudinal section, the axial cell and only two of the three jacket cells are visible. The axial cell is surrounded laterally by jacket cells and is free at the top; it is later divided by a transverse wall into a cover cell and an inner cell. From the jacket cells, without significant participation of the cover cell, the wall of the neck and venter of the archegonium is formed, while the inner (central) cell gives rise to 4–8 neck canal cells, one ventral canal cell, and (at the base) the egg cell. For a different development of archegonia in ferns, see the corresponding section.

³ Protoderm. — Editor's note.

Conducting strands are usually not formed in gametophytes, and are always completely absent in sporophytes. Water transport, for example in Marchantía, occurs through perforated cells in the thallus.

1. Order: Sphaerocarpales⁴. Sometimes the order is even separated into a distinct subclass (Sphaerocarpidae). The thallus⁵ has a simple structure: these are small rosettes growing on the soil (Sphaerocarpos, Fig. 11.109, A) or vertical thalli living in water, consisting of an axis (midrib) with a "wing" extending from it to one side (Riella, Fig. 11 109, B). Archegonia and antheridia are surrounded by pear-shaped involucres opening at the top. The sporogonium wall consists of a single layer of cells that disintegrates upon maturation. In Sphaerocarpos (a plant widely used in genetic experiments), sex chromosomes were first identified (1917) in the plant kingdom. In this genus, as in some other bryophytes, sex determination occurs during meiosis of the spore mother cells.

⁴ It is advisable to separate it into a distinct class. — Ed. note.

⁵ Modern data show that these are peculiar shoots rather than thalli. — Ed. note.

Fig. 11.109. Marchantiopsida, Sphaerocarpales: A — Sphaerocarpos michelii, ♀ thallus with gametangial involucres (5x); B — Riella helicophylla, ♀ thallus (2.5x)

2. Order: Marchantiales. Representatives of the order have a highly differentiated thallus. As an example, we can consider the common liverwort (Marchantia polymorpha, family Marchantiaceae), which is widespread in damp places. It forms ribbon-like, flattened, somewhat fleshy, dichotomously branched thalli (see Fig. 11.111, A, G) up to 2 cm wide with a weakly defined midrib. They grow by division of a group of meristematic cells at their tips. On the underside of the thallus, there are single-layered ventral scales (amphigastria) and negatively phototropic unicellular rhizoids (Fig. 11.110, G), which anchor the thallus to the substrate and conduct water along it (mainly by capillary action between the rhizoids, like a wick; partly through water absorption by them)¹.

¹ The functions of anchoring the plant and absorbing water are performed by smooth rhizoids, while water conduction is carried out by pegged rhizoids. — Ed. note.

Fig. 11.110. Marchantiales, Marchantia, M. polymorpha: A — F — vegetative reproduction: A — section through a gemma cup (12x), B — gemma in surface view (80x), C — in transverse section; D — F — development of a gemma (300x); G — transverse section of the thallus (200x); H — air pore, top view (200x); J — development of assimilation chambers; a — assimilators; as — point of detachment of the gemma; o — upper epidermis with an air pore (pore); ok — oil body; óz — oil cell; г — rhizoid; ri — rhizoid initial; s — stalk cell; и — lower epidermis; v — ventral scale; w — wall thickenings of water-storing cells

Beneath the epidermis of the upper side, which is covered by an almost waterproof cuticle, there are extensive intercellular spaces (see Fig. 11.110, G, J) — "assimilation chambers". They are separated from each other by partitions consisting of one or two layers of cells. On the surface of the thallus, these partitions are visible as light lines dividing dark green rhombic or hexagonal areas. Numerous short, branched assimilators consisting of rounded cells arise from the floor of the chambers; they contain chloroplasts and form the assimilatory tissue ² (see Fig. 11.110, G). Each chamber communicates with the surrounding air through a barrel-shaped pore. In Marchantia polymorpha, it consists of four rings arranged one above the other, each formed by 4 cells. In the event of water shortage, the pore may even narrow slightly, but this is not yet of significant importance for water regulation. Their structure prevents water from entering the "pore". In the entire plant kingdom, there is hardly another gametophyte with such a perfect assimilation and transpiration apparatus (see Fig. 11.122, A). Large, chlorophyll-poor parenchymatous cells on the lower side of the thallus serve as storage tissue (for example, they contain oil bodies, Fig. 11.110, G: ok).

² It is incorrect to call the complex of assimilators a tissue. — Ed. note.

Along the midrib on the upper side, the thallus usually grows in places into cup-shaped structures with dentate margins — gemma cups (Fig. 11.110, A; 11.111, A) containing A number of flat gemmae inside. The latter arise, as shown in Fig. 11.110, D — F, by the outward growth and subsequent division of individual surface cells; they sit on a stalk cell (s), from which they later detach (B: as). In each lateral notch, they have a growing point and consist of several layers of cells (C), some of which are colorless and represent the initials of future rhizoids (C: ri). Gemmae grow into new thalli and very successfully ensure the vegetative reproduction of gametophytes.

Life cycle. Gametangia are located on special vertical branches of the gametophyte thallus (gametangiophores, or receptacles) (see Fig. 11.111, A, G). In their lower part, the gametangiophores resemble a tubular stalk, and in their upper part, they branch repeatedly in a dichotomous manner, forming star-shaped "umbrellas". Antheridia and archegonia arise on different plants (dioecy). Sex determination is carried out, as in many other bryophytes, haplogenotypically via sex chromosomes (analogous to that shown in Fig. 10.19). In the stalk of the receptacle, rhizoids originating from its ventral side end up inside the tube when the edges of the stalk roll inward (Fig. 11.111, B, C); they reach the underside of the thallus and absorb water by capillary action, like a wick.

Fig. 11.111. Marchantiales, Marchantia, M. polymorpha, sexual reproduction: A — ♂ plant with gemma cups and antheridiophore; dots on the thallus surface are air pores (1.5x); B — transverse section through the stalk of an antheridiophore slightly below the "umbrella" (13x), right — dorsal side with air chambers, left — ventral side with two grooves where rhizoids run; C — longitudinal section through an antheridiophore (18x); D — development of antheridia (160x); E — almost mature antheridium, longitudinal section (160x); F — spermatozoid (400x); G — ♀ plant with archegoniophores (1.5x); H — longitudinal section through an archegoniophore; behind the row of archegonia — pseudoperichaetium (25x); J — development of archegonia (160x); K — longitudinal section through a young sporogonium, still enclosed in the archegonium wall, surrounded by a pseudoperianth (35x); L — sporogonium released from its coverings, with spores and elaters protruding; at the base of the foot, a remnant of the archegonium wall is preserved (110x); M — spores and elater (160x)

Antheridiophores terminate in a horizontal "umbrella", which, as a result of threefold dichotomous branching, becomes 8-lobed along the margin (see Fig. 11.111, A). On the upper side, antheridia are developed, each embedded singly in a flask-shaped cavity that opens to the outside via a narrow pore (C). These cavities are separated from each other by assimilation chambers. The dehiscence of antheridia and the release of spermatozoids occur after rain as a result of the antheridium walls becoming mucilaginous and dissolving. Spermatozoids (Fig. 11.111, F) collect on the antheridial receptacle in water droplets (dew or rain) and are retained there by the slightly upturned margin of the receptacle.

Archegoniophores (G) are very similar to antheridiophores at the very beginning of their development. Archegonia are initiated in eight radial rows, with the distance between the two rows facing the DORSAL SIDE OF the stalk being greater than between all the others. During development, the margin of the young "umbrella" gradually curves downward, so that the groups of archegonia end up on its underside (whereby the initially acropetal initiation of archegonia becomes basipetal). Finally, the tissues located between the groups of archegonia grow into secondary lobes of the "umbrella" (nine in total!); two of these develop between the two groups of archegonia that are furthest apart (see above).

Fertilization occurs during rainy weather, when splashes from raindrops containing spermatozoids are transferred from ♂ to ♀ "umbrellas". The epidermal cells of the latter project forward as papillae¹ and form a surface capillary system. Along this system, spermatozoids are conducted to the archegonia, to which they are then attracted by chemotaxis — probably by specific Proteins (see 8.2.1.1).

¹ These are not papillae of epidermal cells, but a special single-layered structure, the pseudoperichaetium. — Ed. note.

Sporophyte. A few days after fertilization, the zygote begins to develop into a multicellular embryo, which grows into a small, oval, greening sporogonium with a very short seta (Fig. 11.111, K, L).

Of the two cells arising after the First Division of the zygote, the upper one (facing the neck of the archegonium) gives rise to the rounded capsule (exoscopic embryo development), while the lower one forms the foot and the seta (L). Initial Selection/3.html">Stages of development are not entirely identical in representatives of different genera and families. By periclinal walls, the capsule primordium is divided into inner and outer cells (K); the inner ones give rise to the multicellular sporogenous tissue (archesporium).

The capsule in Marchantia has a wall of a single cell layer with annular wall thickenings. Only at the apex is the wall two-layered. The capsule dehisces at the apex by several Teeth. The mature capsule is initially covered for some time by the expanding archegonium wall (K), which, however, ruptures as the seta elongates and remains at the base as a "collar". In addition, each capsule is surrounded by a thin, membranous "individual involucre" (= perichaetium)¹ with four or five teeth along the margin, which begins to grow as a sac from the short stalk of the archegonium even before fertilization (H, K). Finally, each radial row of archegonia is further surrounded by an outgrowth of the thallus — a "collective involucre" (involucrum) in the form of delicate teeth (H)².

¹ In Russian literature, the "individual involucre" is called the perianth, and the "collective involucre" is called the perichaetium. — Translator's note.

² It is a plate with a fringed margin, not teeth. — Ed. note.

The capsule releases several hundred thousand spores (L, M). Interspersed among the spores are unicellular, filamentous, thin-walled elaters with spiral

thickenings (M; for their development, see the introduction to Marchantiopsida). Upon dehiscence of the capsule, these elaters perform hygroscopic movements, loosening and dispersing the spore mass (L). Each spore germinates into a very short, chlorophyllous filament (protonema), which initially grows by means of a two-sided apical cell, and later in a more complex manner, develops into a thallus.

Conocephalum conicum (Conocephalaceae), which also grows on rocks and damp soil, resembles Marchantia in its thallus structure, but has simpler stomata and lacks gemma cups. Spermatozoa are discharged from the antheridiophore up to several centimeters upward by turgor pressure. Lunularia (Lunulariaceae) has crescent-shaped gemma cups and sessile antheridiophores. In the smallest representative of this group, Monocarpus sphaerocarpus (Monocarpaceae; Australia), a highly reduced thallus bears a single spherical sporogonium surrounded by a relatively well-developed envelope.

Members of the family Ricciaceae are more simply structured (Fig. 11.112). Dichotomous branching of the thallus by means of two-sided apical cells (see Fig. 5.12) usually follows in rapid succession, resulting in small rosettes¹ (Fig. 11.112, A). In some species, the thallus is partitioned into air chambers and has simple stomata; however, in most species, the upper part of the thallus consists of vertical rows of cells, each ending in a larger, colorless cell (C). The gametangia, as well as the sporophyte (which lacks a foot and seta), are embedded in the thallus¹ (C). Most Riccia species are terrestrial forms (A); the ribbon-like, dichotomously branched R. fluitans (B) lives submerged, while Ricciocarpos natans floats on the water surface like duckweeds.

¹ They are located in depressions on the thallus surface, rather than inside it. — Ed. note.

Fig. 11.112. Marchantiales, Riccia: A — R. glauca, below: plant with sporogonia (2x); B — R. fluitans, submerged aquatic form (2x); C — R. glauca, transverse section through the thallus with an antheridium (125x)

2. Class: Jungermanniopsida (= Hepaticae p.p., predominantly leafy liverworts)

This class includes thalloid and leafy forms, with transitional types between them. The former are weakly differentiated morphologically and anatomically; on their underside, they bear only smooth rhizoids. The gametophytes of leafy forms bear simple leaves without a midrib, arranged in two rows².

² With rare exceptions, the phyllotaxis of Jungermanniopsida is three-ranked. — Ed. note.

Members of the class Jungermanniopsida are often interpreted as an evolutionary series from thalloid to leafy forms. However, leafy forms can also be considered ancestral, with thalloid forms derived from them by assuming the fusion of overlapping leaves and flattening of the stem during evolution.

Gametangiophores are absent in the gametophytes. Oil bodies are usually present in large numbers in all cells, whereas in Marchantiopsida they are localized in specialized oil cells. The sporogonium capsule is elevated on a long seta (an adaptation for wind dispersal of spores) and usually dehisces by 4 Valves (see Fig. 11.114, A). In the previous subclass, the sporogonia lack setae or have very short ones. The elaters are similar in structure and development to those of the previous class. Conducting bundles are absent in the sporophyte; in the gametophyte, they occur rarely and are then very simple, i.e., composed solely of hydroids (Symphyogyna, Haplomitrium).

1. Order: Metzgeriales. The thallus, which grows by means of a single apical cell (see Fig. 5.12, B, C) and is most often dichotomously branched, consists of one or several layers of uniform cells; in some species, it has a midrib of elongated cells (see Fig. 11.114, A, B), and Symphyogyna even possesses a primitive central conducting strand. The genus Fossombronia is distinguished by two rows of obliquely attached leaves that are multistratose at the base. Thus, we have here a transition from thalloid to leafy forms. Archegonia develop below the apical cell, which continues its further growth; sporophytes, surrounded by a pseudoperichaetium, sit on the thallus (A) or on short lateral branches ("anacrogynous"). In species of some genera, elaters are attached like a brush to the upper ends of the capsule valves (Metzgeria, A) or in the center of its base (Pellia). Most of the 500 species of this order, for example, species of the genera Riccardia, Pellia, Fossombronia, inhabit moist soil. In contrast, Metzgeria grows on shaded rocks or as an epiphyte on the bark of deciduous trees. According to recent studies, the genus Blasia (see Fig. 11.114, C) occupies an isolated systematic position between Jungermanniopsida and Marchantiopsida and therefore, strictly speaking, should belong to a separate class (Blasiopsida). In Blasia, the thallus has flask-shaped gemma receptacles; it is divided along the margins into leaf-like lobes and bears small scales on the underside.

2. Order: Calobryales¹. Vertical stems bear three rows of identical leaves and are attached to the substrate by fleshy, branched "rhizomes" that lack rhizoids but contain endotrophic fungi ("mycorrhiza"). In particular, Haplomitrium (see Fig. 11.113, C), which also occurs in Europe, has flat leaves that are multistratose at the base, and a central strand in the cauloid.

¹ This group, with even greater justification than Blasia, should be separated into a distinct class. — Editor's note.

Fig. 11.113. Takakia lepidozioides (A — B) and Haplomitrium hookeri (C): A — habit (6x); B — transverse section of the stem (100x); C — Jungermanniopsida, Haplomitrium (6x)

3. Order: Jungermanniales. Members of this order are predominantly tropical plants, mostly small, living on soil and tree trunks, and in the tropics also on the leaves of forest trees. Numbering about 9,000 species (250 in Central Europe), they constitute approximately 90% of all liverworts. Their body is clearly differentiated into a prostrate or ascending, branched, dorsiventral stem and unistratose leaves without a midrib, which are arranged in two rows² along the sides of the stem at an angle to it (Fig. 11.114, D — J). There are no conducting tissues in the stem. Jungermanniales have neither air pores (as in Marchantiales) nor true stomata (as in Anthocerotales).

² The leaves are most often arranged in three rows. — Editor's note.

The leaves, which are obliquely attached to the stem and therefore arranged like roof tiles, overlap each other in different ways and are highly diverse in shape. They are called succubous when the lower margin of each leaf is covered by the upper margin of the leaf situated below it (Fig. 11.114, E, F), and incubous if the lower margin is not covered when viewed from above (H). Leaves can have a rounded or pointed apex (G), be emarginate (F), bidentate or pluridentate, bilobed (H), or dissected into filiform segments (D). In the epiphytic Frullania (J), one of the two leaf lobes is modified into a cup-shaped structure that serves to retain water ("water sac").

In most genera, along with the dorsal leaves arranged in two rows, there is also a row of smaller and differently shaped leaves on the ventral side — these are amphigastria, or underleaves (for example, in Frullania, Calypogeia, Fig. 11.114, E, J). The formation of three rows of leaves is due to the presence of a three-sided pyramidal apical cell of the shoot, one side of which, however, produces only small leaves or — in species with two rows of leaves — does not produce leaves at all. Lateral branches arise adjacent to the leaves.

The archegonia, located at the tip of the shoot (acrogynous), are surrounded by a perianth (Fig. 11.114, G), which consists of three fused upper leaves. In some species, the gametophyte cells beneath the fertilized archegonium divide, forming a sac-like receptacle (marsupium) to protect the young sporophyte that grows after fertilization of the egg cell. The sporogonium is already fully developed when, due to the elongation of its seta (see 7.1.1), it ruptures the wall of the archegonium, which remains as a leathery sheath at its base. There is no columella in the capsule. The cell walls of the multilayered capsule wall have ring-like or bar-like thickenings, or are uniformly thickened (except for the thin outer cell walls); dehiscence occurs due to surface tension forces as the cells lose water (see 8.4).

The protonema of Jungermanniales is structured differently in various genera, but usually consists of only a few cells. In Metzgeriopsis pusilla, on the contrary, it is thalloid and is essentially the main vegetative body, bearing tiny plants with few leaves that serve only for the formation of sex organs. In Protocephalozia, the filamentous protonema bears antheridia and archegonia¹.

¹ As in Metzgeriopsis, in Protocephalozia ephemeral gametophore shoots are formed on the long-lived protonema, which in turn bear the sex organs. Sex organs are never formed directly on the protonema. — Editor's note.

Vegetative reproduction is also widespread in Jungermanniales: in some, it occurs by means of easily detached caducous branches and specialized gemmiferous leaves (common in tropical epiphyllous Lejeuniaceae), in others — by means of gemmae, which are formed mainly along the margins or at the tips of leaves and consist of a few cells or only a single cell (see Fig. 11.114, H).

The Jungermanniales also include: Scapania, Lophozia, and Trichocolea (see Fig. 11.114); Lophocolea (see 7.1.1.); and Cephalozia (see Fig. 8.38).

Fig. 11.114. Jungermanniopsida: A — C — Metzgeriales:

A — Metzgeria conjugata (ventral side) with several ♂ and one ♀ thallus branches, elater tufts on the 4 capsule valves, the seta of the sporogonium is surrounded by a pseudoperichaetium (15x), B — M. conjugata, transverse section of the thallus (30x), C — Blasia pusilla, with flask-shaped gemma cups and numerous auricles on the dorsal side of the thallus inhabited by Nostoc (4x); D — J — Jungermanniales: D — Trichocolea tomentella, leaf and underleaf (a) (7x), E, F — Calypogeia trichomanis: E — plant, dorsal view, with marsupium and mature sporogonium (2x), F — fragment with 4 leaves and 2 underleaves, ventral view (6x), G — Scapania undulata with perianth and mature sporogonium (2x), H — Lophozia ventricosa, dorsal view, with groups of gemmae at the leaf tips (10x), J — Frullania dilatata, ventral view, with "water sacs" (25x)

Evolution. The taxonomic position of Jungermanniopsida is controversial. Previously, based on DNA analysis, they were assumed to be evolutionarily closer to Bryopsida than to Marchantiopsida. Recent studies confirm their independence as a distinct class, but at the same time point to a closer relationship with Marchantiopsida than with Bryopsida, so that both classes (along with Blasiopsida, but not Anthocerotopsida) form a higher-rank taxon. According to this new concept, which is not yet used here, bryophytes are divided into three main groups: Hepaticophytina (liverworts), Bryophytina (mosses), and Anthocerotophytina (hornworts).

3. Class: Bryopsida (= Musci, mosses)

The gametophyte of mosses is always differentiated into stem and leaves. It is anchored in the soil or litter by means of usually branched, multicellular rhizoids with oblique cross-walls (in the previously discussed bryophytes, these are unbranched and almost always unicellular) (see Fig. 11.123, E). In contrast to the leafy species of Jungermanniales, the shoots are not dorsiventral but radially symmetrical, and the leaves are usually spirally arranged, appearing three-ranked or many-ranked when viewed from above. Lateral branches arise below the leaf (cf. Fig. 5.13; unlike in seed plants). The leaves, which grow by means of a two-sided apical cell, often have a midrib, and they lack oil bodies (leafy liverworts often have oil droplets, and their leaves grow by means of a one-sided apical cell).

In mosses with prostrate shoots, the spirally arranged leaves are turned to one or both sides, creating a distinction between the dorsal and ventral sides, though in a different way than in liverworts (e.g., Fissidens, see Fig. 11.126, С).

Mosses also differ from other bryophytes in their sporophyte: it usually has stomata and develops as a capsule with a columella, typically on a long seta¹. Elaters are absent.

¹ Like in other bryophytes, it also has a foot (haustorium). — Editor's note.

Life cycle. The spores of mosses germinate into gametophytes, which initially appear as an abundantly branched, positively phototropic green filament—the protonema (see Fig. 11.123, A). When growing en masse, protonemata are visible to the naked eye as a green felt. First, filaments rich in chloroplasts with cross-walls perpendicular to their axis develop; these are called chloronema. The chloronema gradually transitions into a substrate-creeping caulonema, which is poorer in chloroplasts and has oblique cross-walls. Under sufficient light, buds develop on the caulonema, most often on its short lateral branches, giving rise to the moss plants¹ (see Fig. 11.123, A). In addition, numerous, mostly upright lateral branches of the chloronema type arise from the caulonema. A bud arises in such a way that, after one or two stalk cells are cut off, the swelling terminal cell cuts off a three-sided pyramidal apical cell (B, C) by oblique walls, which, by producing segments, develops into a leafy moss plant. Where such buds are numerous, the moss plants form dense cushions.

¹ The protonema represents the juvenile form of the moss plant. It is not the moss plants that develop on it, but gametophores. — Editor's note.

Sex organs in mosses are arranged in groups at the tips of the main shoot or smaller lateral branches. They are surrounded by the uppermost leaves, which are often modified into a special "involucre"—the perichaetial leaves² (Fig. 11.115).

² Perichaetial leaves surround only the archegonia. Around the antheridia are the perigonial leaves. — Editor's note.

Fig. 11.115. Bryopsida: A — G — Development of the antheridium in Funaria hygrometrica: A — transverse division of the antheridium primordium, B — formation and C — division of the apical cell, D — differentiation into the jacket and the primordium of the spermatogenous tissue, E — the same, in transverse section (A — E — 650x), F — nearly mature antheridium (300x), G — Cytology/practical/54.html">Longitudinal section of an antheridial group of Mnium hornum, some antheridia seen from the surface, some in section (100x); H — L — development of the archegonium in Mnium undulatum (250x): H — stalk without archegonium primordium yet, J — the archegonium (a) is initiated by the formation of a central cell (dotted), a cover cell (d), and wall cells, K — the central cell has divided into an egg cell and a ventral canal cell, L — numerous neck canal cells are cut off from the cover cell; h — bracts; p — paraphyses; s — stalk

Mosses can be bisexual (hermaphroditic), monoecious, or dioecious, depending on whether the antheridia and archegonia develop on the same or on different shoots of the same plant, or on different plants.

A number of multicellular paraphyses, often with rounded terminal cells, are usually interspersed among the sex organs.

Antheridia and archegonia of mosses are stalked, and unlike in other bryophytes (and archegoniates in general) (Box 11.8, p. 204), their body is formed from segments cut off by an apical cell (see Fig. 11.115).

Sporophyte. After fertilization of the egg cell by a chemotactically attracted sperm (see 8.2.1.1), the zygote first undergoes multiple transverse divisions, developing into an elongated, segmented embryo. In typical development, oblique walls arise in its uppermost cell, cutting off a wedge-shaped, two-sided apical cell (Figs. 11.116; 11.117, A, B; 11.118). This cell cuts off segments on both sides, which divide further. In the cells of the segments that form the capsule, a division wall appears along a vertical radial plane, so that four quadrants are visible in the transverse section of the embryo (see Fig. 11.117, C). From these, divisions by periclinal walls give rise to outer (amphithecium) and inner (endothecium) cells (Fig. 11.117, C, D: a, e). The outermost layer of the endothecium usually differentiates into the archesporium (E, F: ar), which completely divides into spore mother cells (G; sm). Each spore mother cell undergoes meiotic division to produce four haploid spores. In contrast to Marchantiopsida, the inner cells of the endothecium do not participate in the Formation of the archesporium, but usually form a strand of sterile tissue—the columella (Fig. 11.117, E: co; 11.119, A: c), surrounded by the archesporium (Fig. 11.119, A: sz).

Fig. 11.116. Bryopsida, Buxbaumiales: A — C — Buxbaumia aphylla: A — ♀, B — ♂ gametophytes (A, B — 35x), C — sporophyte; D — Diphyscium sessile

Fig. 11.117. Bryopsida, development of the sporogonium of Funaria hygrometrica: A, B — longitudinal section, first divisions of the zygote; C — E — transverse section: C — divisions in the endothecium (e) and amphithecium (a), D — further divisions, E — more mature sporogonium; in the endothecium, the outermost cell layer — the archesporium (ar) — separates from the columella (co) (A — E — 300x); F, G — transverse section through the archesporium (ar) and the not yet isolated spore mother cells (sm) arising from it (250x); s — apical cell

The columella serves to conduct nutrients and store water for the developing spores; nutrients are also supplied to the spores by the nutrient-rich cells surrounding the archesporium. The lower part of the embryo (Fig. 11.118, A) — the foot (haustorium) — is anchored in the tissue of the gametophyte.

The young sporophyte (embryo) is initially enclosed in a sheath (embryotheca), which is formed from both the venter of the archegonium and the tissue of its stalk, and even from the stem tissue. As the sporophyte grows, the embryotheca, unable to withstand the tension, ruptures transversely. The upper part is carried up on the apex of the sporophyte as a calyptra, while the lower part remains as a vaginula (Fig. 11.118, B).

Fig. 11.118. Bryopsida:

A — longitudinal section of a young sporophyte of the moss Pogonatum urnigerum (150x); numbers indicate successive segments; segments 1 — 7 form the foot of the sporophyte; B — Pottiales, Pottia lanceolata (40x), upper part of the shoot, leaves removed, two archegonia fertilized: the embryo on the left, due to the elongation of the seta (s), has lifted the upper part of the embryotheca as a calyptra (к), leaving the lower part as a vaginula (v); the embryotheca on the right is still intact; а — unfertilized archegonium; SM — initiation of the seta meristem

At the upper end of the mature capsule, a specialized structure is formed — the annulus, designed for capsule dehiscence and spore dispersal. The seta elevates the capsule so that the wind can easily disperse the spores. In the young sporogonium, active assimilatory tissue is located external to the spore mass and is covered by the epidermis¹.

¹ The assimilatory tissue is located significantly deeper than the epidermis. It directly adjoins the epidermis in the apophysis — the part of the sporogonium between the capsule and the seta. — Editor's note.

Fig. 11.119. Bryopsida, Bryidae: A — longitudinal section through the sporogonium of the moss Funaria hygrometrica (25x); B — assimilatory tissue with a stoma (90x); a — annulus; аg — assimilatory tissue; с — columella; d — operculum; р — peristome; s — stoma; sz — sporogenous cells

Stomata of the Mnium-type (Fig. 11.119, A, B), which is also characteristic of ferns, occur on the sporogonium. In different families, they vary significantly in number (from 3 to 300 per capsule), shape, and size.

Conducting strands. Some species possess simple conducting tissues. These can be present in both gametophytes and sporophytes. As in the vascular bundles of vascular plants, conduction is carried out by a chain of different cells. Water and salts are transported by hydroids — elongated, dead cells that, when fully mature, lack a nucleus and cytoplasm, and have thickened lateral walls and oblique end walls. Unlike the tracheids of vascular plants, their cell walls are neither lignified nor reinforced with annular or spiral thickenings. Assimilation products are conducted by other, likewise elongated cells — leptoids, which resemble the sieve elements of vascular plants in Development and Structure. Their lateral walls are often thickened and, to a lesser extent than the sometimes oblique end walls, are perforated by sieve pores with plasmodesmata. Until they die back, leptoids retain nuclei and plastids in their cytoplasm. Usually, hydroids are located internally and leptoids externally; they are often mixed with other elements in the central strand. The latter is surrounded by tissues of thin-walled (inner cortex) and thick-walled (outer cortex) cells. Stereids — are living, nucleated, and plastid-containing, elongated cells adjacent to the hydroids. Their thickened but non-lignified walls provide mechanical strength (comparable to collenchyma cells). Parenchyma cells bordering the leptoids, despite great Structural and functional similarity, differ from them by the absence of sieve pores in their end walls. Various deviations from this type of strand occur — ranging from structural simplification (for example, in the absence of leptoids) to complete reduction of the strands.

Leaf trace strands (see Fig. 11.123, H), which join the central strand or end blindly in the cortical parenchyma, extend into the leaves as the conducting tissue of their midrib. Only when there is a direct connection between the hydroids of the leaf and the central strand of the cauloid, i.e., in the presence of true leaf traces, are the prerequisites met for a continuous water conduction system. Simplifications of the conducting system of leaves are common: for instance, there may be very few or no hydroids at all in the cortical parenchyma of the cauloid. In the conducting strands of leaves, wide-lumen parenchyma cells apparently serve to conduct assimilates, whereas typical leptoids are rare here (Polytrichales).

For the Nutrition of the sporophyte, its attachment to the gametophyte is of great importance. Serving as an absorptive organ, the haustorium penetrates into the greatly proliferating tissue of the archegonial stalk, and in some cases (Polytrichum) — even deep into the stem tissue down to its central strand. The hydroids of the sporogonium foot closely adjoin the hydroids of the gametophyte stem. Rhizoid-like appendages that penetrate the gametophyte tissue are sometimes found on the haustorium of the sporogonium, but more often there are transfer cells, which adjoin parenchyma cells or leptoids and are characterized by surface-increasing wall thickenings in the form of protuberances or ridges. In contrast, cytoplasmic connections (via plasmodesmata) between the sporophyte and gametophyte are absent. Often, the junction of tissues between the gametophyte and sporophyte is rather imperfect.

Vegetative reproduction. Mosses possess an extremely high regenerative capacity. Thus, broken stems and leaves can grow into new plants either directly or via a protonema stage. In some species, groups of cells develop in the leaf axils and at the shoot tips, which can shed as "gemmae" (see Fig. 11.126, O).

The mosses (Bryopsida) are divided into three subclasses (Sphagnidae, Andreaeidae, Bryidae). In the first two subclasses, the sporogonium capsule is elevated by means of a haploid pseudopodium (an elongated archegonial stalk¹).

¹ The pseudopodium has a more complex nature, including part of the stem tissues. — Editor's note.

1. Subclass: Peat Mosses (Sphagnidae)

The subclass includes only one family — Sphagnaceae, with a single but extremely species-rich (over 200!) genus, Sphagnum. Sphagnum inhabits boggy, predominantly lime-poor areas, often with low pH values, where it forms large cushions and carpets that grow upward year after year, while their lower part dies off and gradually turns into peat. Lignin-like substances are deposited in the cell walls.

In the presence of certain mycorrhizal fungi, the tetrahedral spores germinate into a protonema; initially filamentous, it subsequently develops into a small, lobed, single-layered thallus with filamen

tous rhizoids. The thallus usually produces only a single gametophyte with a tuft of rhizoids at its base (Fig. 11.120, D).

Fig. 11.120. Bryopsida: A — H — Sphagnidae, Sphagnum:

A — S. acutifolium, plant with sporogonia (2/3x), B — S. squarrosum, mature sporogonium at the tip of a branch (10x), C — S. acutifolium, young sporogonium in longitudinal section (17x), D — S. acutifolium, protonema with a young plantlet (100x), E — S. molluscum, portion of a branch with retort cells that accumulate water; leaves removed (10x), F — the same, in transverse section (10x), G — S. acutifolium, portion of a single-layered leaf; showing large hyaline cells with annular thickenings and pores, and small chlorophyll-containing cells between them (300x), H — the same, in transverse section (300x), J — K — Andreaeidae, Andreaea rupestris: J — habit of plant (8x), K — longitudinal section through a young sporophyte (40x); ah — neck of archegonium; aw — embryotheca; с — columella; d — operculum; f — foot/haustorium; к — calyptra; ка — capsule; pb — perichaetial leaves; ps — pseudopodium; s — spores; sf — haustorium of sporogonium; sg — sporogenous tissue; w — capsule wall

The erect, rhizoid-free stems are almost always arranged in dense tufts and bear fascicles of lateral branches at regular intervals. In each fascicle, some branches spread outward and upward, while others hang downward, closely appressed to the stem (Fig. 11.120, A). At the apex of the shoot, the branches form a dense HEAD (capitulum). Due to cell wall pigments, some Sphagnum species (especially those inhabiting raised bogs) are colored brown or bright red. Each year, one of the branches at the shoot apex develops as vigorously as the corresponding growth of the mother shoot, resulting in false dichotomous branching (pseudodichotomy). As the stems gradually die off from below, the daughter branches become independent plants.

The stem cortex consists of a single- or multi-layered tissue of dead, empty cells that absorb water by capillarity; their lateral and transverse walls often have rounded pores (Fig. 11.120, E). The leaves also contain cells with perforated walls reinforced by annular or spiral thickenings (Fig. 11.120, G); these are situated individually within the meshes of a single-layered network of elongated, living, chloroplast-containing cells. These unique structures serve for the absorption of water and minerals; the plants can thus retain water in amounts exceeding their dry weight by about 20 times. The leaves lack a midrib, and the stems lack a central strand.

Reproduction. Certain branches of the capitulum have a distinctive appearance and coloration. They produce the sex organs. In the leaf axils, male branches form globose, long-stalked antheridia (the gametes emerging from them were the first plant spermatozoids to be discovered); female branches bear archegonia at their tips, which, unlike those of other mosses, develop without an apical cell — similar to liverworts. The sporogonia develop only a very short foot with an expanded haustorium. They remain enclosed within the embryotheca for a long time, eventually rupturing it at the apex and leaving it at their base as a collar (Fig. 11.120, B: aw). In the spherical capsule, the sporogenous tissue (C: s) covers the hemispherical columella like a dome. The archesporium originates not from the endothecium, but from the innermost layer of the amphithecium. The sporogonium, with its expanded haustorium, is embedded in the swollen tip of the small shoot bearing it; after the sporogonium matures, this tip elongates into a pseudopodium of considerable length, elevating the sporogonium (B: ps). Due to excess air pressure within the capsule, the operculum is blown off with an audible pop, and the spores are shot out to a distance of more than 20 cm.

2. Subclass: Andreaeidae

The only family of the subclass, Andreaeaceae, is represented by three genera. Species of the genus Andreaea (numbering about 120) form small, dense, dark brown cushions on non-calcareous rocks in alpine regions, the Arctic, and the Antarctic. The sporogonium, as in Sphagnum, is elevated on a pseudopodium, which develops from the archegonial stalk. The capsule, initially covered by a calyptra like a cap, dehisces by four longitudinal slits, with the resulting four valves remaining attached to each other at both the apex and the base (Fig. 11.120, J). As in Sphagnum, the bell-shaped sporogenous tissue surrounds the columella (K). The protonema is thalloid and branched. In the genus Andreaeobryum, there is no pseudopodium.

The Takakiales, formerly classified as liverworts, are probably better treated as mosses and included in the Andreaeidae¹. This includes the Asian genus Takakia (see Fig. 11.113, A) with leaves divided to the base into 2 — 4 cylindrical segments, and a central strand in the stem.

¹ It is even better to consider them as the class Takakiopsida. — Editor's note.

3. Subclass: Bryidae

In representatives of this subclass, the capsule is elevated not by a pseudopodium belonging to the gametophyte (as in both preceding subclasses), but by a seta (diploid) formed by the sporophyte.

The gametophyte in this subclass reaches its greatest diversity and highest differentiation among mosses; however, in a few cases, it is almost entirely restricted to the protonema stage (e.g., Ephemeropsis tjibodensis, Viridivellus pulchellum). The shoots either grow vertically and bear archegonia at the apex, and later a capsule on a seta (acrocarpous mosses; see Fig. 11.123, E), or they are plagiotropic and usually pinnately branched, bearing archegonia and later capsules on short lateral branches (pleurocarpous mosses; see Fig. 11.126, R). The stem typically contains a single central strand (see Fig. 11.123, H), which in the most highly developed forms (Polytrichum) reaches significant histological differentiation (see: Systematics, p. 233).

Leaves consist predominantly of a single layer of cells. The marginal cells of the leaf lamina often form a distinct border (see Fig. 11.123, K: outer layer) or teeth. Leaf cells in acrocarpous mosses are usually parenchymatous (isodiametric, see Fig. 11.123, K), whereas in pleurocarpous mosses they are mostly prosenchymatous (elongated, as in Fig. 11.120, G). The apical cell of the leaf in acrocarpous forms produces several daughter cells, which then divide by walls more or less perpendicular to each other, resulting in a network of isodiametric cells. In pleurocarpous species, the daughter cells cut off by the apical cell via oblique walls rapidly divide further into rhombic cells, whose lateral angles elongate, resulting in a network of prosenchymatous cells. Leaves (especially those with a network of prosenchymatous cells) often have a midrib (see Fig. 11.123, J — L).

The capsule in Bryidae also reaches its highest perfection. The sporogonium consists of a slender, elastic seta (see Fig. 11.123, E; 11.126) and a radial (see Fig. 11.123, E) or dorsiventral (see Fig. 11.116, C) capsule, initially covered by a calyptra (the upper part of the embryotheca: see Fig. 11.118, B; 11.123, E, M), which later falls off¹. The neck of the archegonium soon dries up and remains as a spire on the calyptra. The calyptra, therefore, consists not of diploid sporophyte tissue, but of haploid gametophyte tissue (see Fig. 11.108, D). The uppermost part of the seta beneath the capsule is called the apophysis; this is where stomata develop most abundantly. A columella runs along the entire length of the capsule, surrounded by the sporogenous tissue in the form of a hollow cylinder (see Fig. 11.119, A: sz). The columella and sporogenous tissue are further surrounded by large intercellular spaces (see Fig. 11.119), which form in the amphithecium and expand particularly during maturation. The more or less spherical meiospores usually contain numerous chloroplasts (see Fig. 11.123, O).

¹ The sporogonium also includes a haustorium. — Editor's note.

The upper part of the capsule wall develops as an operculum (see Fig. 11.119, A: d; 11.123, M). Beneath the rim of the operculum, there is often a narrow ring-like zone — the annulus (see Fig. 11.119, A: a; 11.124). Its cells contain swelling mucilage and thus ensure the shedding of the operculum when the spores mature (the calyptra falls off even earlier). Along the rim of the urn remaining after the operculum is shed, most mosses have a peristome (see Fig. 11.119, A: p; 11.123, N), which is typically composed of teeth and initially covered by the operculum. In other mosses, the peristome is absent. The STRUCTURE OF THE peristome is highly diverse.

Fig. 11.121. Bryopsida, Bryidae, Leucobryum glaucum: A — gametophyte with sporophytes (natural size); B — leaf structure: two layers of cells devoid of cytoplasm, connected to each other by large Pores in the walls; between them are small, elongated cells containing chloroplasts (300x)

Fig. 11.122. Bryidae, Polytrichales: A — leaf structure of Polytrichum formosum, with lamellae of chlorophyll-containing cells visible on the upper side (250x); B — Polytrichum juniperinum, transverse section of the stem (120x); ar — outer cortex; h — hydroids; i — intercellular spaces; ir — inner cortex; l — leptoids; z — central strand

Fig. 11.123. Bryidae, Bryales, Mnium punctatum: A — protonema with a bud (20x); B — development of a bud on the protonema; chloroplasts in the upper cells are not shown (80x); C — initiation of a three-sided apical cell (85x); D — ♂ plant (natural size); E — ♀ plant with sporophyte (natural size); F — longitudinal section of the antheridial group (15x); G — longitudinal section of the archegomial group (15x); H — transverse section of the stem with a central strand and three leaf-trace strands (40x); J — leaf (4x); K — leaf tip (25x); L — transverse section of the lower part of the leaf (50x); M — mature capsule, with operculum and calyptra nearby (4x); N — peristome; on the left, the outer peristome is removed; one of the three teeth of the outer peristome is bent back when dry (30x); O — spore (100x)

In a few mosses (Polytrichales, Tetraphidales, see Fig. 11.126, N), the peristome teeth consist of rows of whole cells. In all other mosses, however, the peristome is formed beneath the operculum from the thickened parts of the cell walls of the three innermost layers of the amphithecium.

The development of such a peristome can be traced in transverse (Fig. 11.124, B) and longitudinal (Fig. 11.124, A) sections of the upper part of the capsule. The tangential walls between the First and Second cell layers become particularly heavily thickened, while the walls between the second and third layers are less thickened; the radial walls, as well as the unthickened parts of the tangential walls of the three cell layers, eventually break down, so that only the thickened parts of the tangential cell walls remain. These constitute the peristome, which is thus double (Fig. 11.123, N) and consists not of whole cells, but only of the persistent tangential walls. The outer peristome consists of 16 transversely striated teeth (Fig. 11.123, N) located along the inner rim of the urn wall; the inner peristome ("cilia") is closely appressed to the outer one and is composed of narrow plates and filaments that have transverse thickenings on their inner surface¹ and merge in their lower part into a basal membrane (Fig. 11.123, N; 11.124, A; ip). Between every two teeth of the outer peristome, there are two cilia of the inner peristome² (the group of diplolepideous mosses, as opposed to haplolepideous ones with only a single ring of peristome teeth).

¹ On the outer. — Editor's note.

² The relative arrangement of the elements of the outer and inner peristomes is diverse. — Editor's note.

Fig. 11.124. Bryidae:

A — Funaria hygrometrica, longitudinal section of the upper part of a moss capsule before dehiscence (200x); B — Mnium punctatum, transverse section of the capsule in the region of the peristome (120x); ap — outer peristome; ad — assimilatory tissue; c — columella; d — dehiscence zone; ed — epidermis of the operculum; ek — epidermis of the urn; ip — inner peristome; s — spore mother cells; w — thick-walled cells connecting the teeth of the outer peristome with the epidermis; I — III — cells of the annulus; 1 — 3 — the three innermost layers of the amphithecium

The outer peristome teeth perform hygroscopic movements (see Fig. 8.36; see 8.4), closing or opening the capsule (Fig. 11.123, N) depending on the weather (usually bending outward in dry weather), and in this way facilitate the gradual dispersal of spores. Inclined sporogonia and those with a wide urn Mouth usually have a well-developed peristome, whereas in genera with an erect sporogonium having a narrow urn mouth, the peristome is often reduced (Fig. 11.125, D).

Fig. 11.125. Bryidae, Schistostegales, Schistostega pennata: A — fertile plant bearing a capsule (103x); B — sterile plant (10x); C — fragment of the previous (50x); D — opened capsule (25x); E — protonema ("luminous moss"), side view, with the arrow indicating the direction of light rays (150x); F — the same, top view (150x); G — gemma on the protonema (150x); H — pathway of light rays within a protonemal cell

Since young sporophytes can be induced to regenerate a protonema, it is likewise possible to obtain diploid gametophytes, which in turn can produce tetraploid sporophytes. By repeating this process multiple times, researchers have successfully generated gametophytes with a 16-fold chromosome set. Chromosome counts in numerous species have revealed that moss gametophytes frequently contain double to quadruple sets of chromosomes per nucleus and are thus often polyploid; in such cases, the sporophyte contains twice as many chromosomes as the gametophyte.

Systematics. The systematic Classification of the subclass Bryidae, which comprises approximately 15,000 species, is based on the characteristics of both the gametophyte and the sporophyte (particularly the peristome).

1. Superorder: Polytrichanae. The peristome consists of intact horseshoe-shaped or elongated fibrous cells. Shoots are acrocarpous, featuring highly differentiated conducting tissue (a continuous water-conducting system). Subterranean "rhizomes" differ from the aerial parts of the gametophyte by having an approximately radial arrangement of water-conducting hydroids, thus resembling the roots of dicotyledonous flowering plants. The upper surfaces of the leaves bear longitudinal lamellae composed of chloroplast-rich cells ("assimilation plates", see Fig. 11.122).

1.1. Order: Dawsoniales. Turf-forming mats of slender plants up to 70 cm tall, found in Australia and other Regions of the Southern Hemisphere.

1.2. Order: Polytrichales. Unlike the species of the preceding order, the opening of the urn is initially closed by a thin membrane (the epiphragm). Polytrichum (Fig. 11.126, T), featuring needle-like leaves and reaching heights of up to 40 cm, grows on soil in forests and bogs. In Pogonatum, the protonema is long-lived. Atrichum undulatum, with its wavy, Tongue-shaped leaves, is a moss frequently encountered on forest soil.

2. Superorder: Dicrananae. The peristome, unless entirely reduced, is single (haplolepidic). Predominantly acrocarpous mosses.

2.1. Order: Dicranales. The peristome typically consists of 16 pairwise united teeth. Dicranum species, distinguished by their sickle-shaped leaves, commonly inhabit forest soils. In Leucobryum, the costa occupies almost the entire leaf and consists of two cell types: living green cells and dead water-storing hyalocysts (see Fig. 11.121). It inhabits acidic forest humus. This group also includes Archidium (see Fig. 11.126, A), which possesses a sporogonium lacking a seta, operculum, and peristome. The capsule opens irregularly by decay (cleistocarpy).

2.2. Order: Fissidentales. Leaves are arranged in two rows, bearing a dorsal wing. In Germany, species of the genera Fissidens (Fig. 11.126, C, D) and Octodiceras are represented.

2.3. Order: Pottiales. Leaf cells feature nodular thickenings on their outer walls ("papillae"). Tortula possesses a long, spirally twisted peristome (Fig. 11.126, F). Eucladium (see: Occurrence and lifestyle of mosses, p. 228) predominantly forms cushions encrusted with lime.

2.4. Order: Grimmiales. Predominantly cushion-forming inhabitants of rocky substrates that lack the diagnostic Features of the two preceding orders. The leaves, for instance in Grimmia (Fig. 11.126, H) and Rhacomitrium, often terminate in colorless hairs or hyaline points.

Subsequent superorders are distinguished by a double peristome (diplolepidic).

3. Superorder: Bartramiales comprises acrocarpous mosses. The capsules, such as those in Bartramia and Timmia, are typically inclined, pear-shaped to nearly spherical, and furrowed.

4. Superorder: Funariales. Represented by the globally widespread species Funaria hygrometrica (Fig. 11.126, J), frequently found on burnt ground. This is an acrocarpous moss growing on soil, characterized by large, smooth leaf cells¹. Splachnum luteum (Fig. 11.126, K), which grows like other species of this genus on herbivore dung, is a dioecious species. It is distinguished by the brightly colored, disc-shaped apophysis of the sporogonium. Female plants (♀) are short and squat, with larger leaves compared to male plants (♂); their archegonia are surrounded by appressed perichaetial leaves (whereas in ♂ they are spreading), thus forming a bud-like structure. Sexual Dimorphism is already evident in the protonemas. In Ephemerum, the protonema is persistent.

¹ The Origin of the species epithet hygrometrica is noteworthy: the hygroscopic seta of the sporogonium twists spirally under dry conditions and untwists when moist. — Transl. note.

5. Superorder: Bryales. The inner teeth of the double peristome are highly differentiated (see Fig. 11.123, N). Transitions exist from acrocarpous to pleurocarpous growth forms, as well as between leaves composed of parenchymatous and prosenchymatous cells.

This group includes Bryum, Rhodobryum (see Fig. 11.126, L) with a prominent rosette of leaves, species of the genus Mnium (see Fig. 11.123) which are common on forest soil, and Mittenia plumula (Australia, Tasmania, New Zealand), whose protonema reflects light (cf. "luminous moss").

Fig. 11.126. Bryopsida, Bryidae: A — Archidium phascoides, entire plant (5x) and capsule (20x); B — Dicranum scoparium, three-year-old plant (natural size); C — Fissidens bryoides (4x); D — the same, leaf (15x); E — G — Tortula muralis (4x): F — peristome (30x), G — leaf with hyaline Hair point (10x); H — Grimmia pulvinata (natural size); J — Funaria hygrometrica (2x); K — Splachnum luteum (natural size); L — Rhodobryum roseum (natural size), M — Tetraphis pellucida (2x); N — peristome; O — gemma cup (8x); P — Climacium dendroides (natural size); Q — Hylocomium splendens, four-year-old plant (1/2x); R — Cratoneuron commutatum (1/2x); S — Papillaria deppei (1/2x); T — Polytrichum commune, on the right a young sporophyte covered by a calyptra (1/2x)

6. Superorder: Hypnanae. Pleurocarpy predominates here. Leaf cells are prosenchymatous; the costa (if present), unlike in the species of previous groups, is homogeneous, meaning it consists of cells of a single type.

6.1. Order: Neckerales. The inner peristome of the erect capsule is typically underdeveloped. Climacium (Fig. 11.126, P) branches in a tree-like manner.

Epiphytic species of Papillaria (S) and closely related genera, which are common in the tropics, form "pendulous forms". Fontinalis (see p. 228) has adapted to an aquatic lifestyle. Species of Macromitrium produce larger female (♀) and smaller male (♂) spores within their capsules. Orthotrichum can also be assigned here.

6.2. Order: Hookeriales. The peristome is reduced; leaves are broad and composed of large cells; an example is Hookeria lucens, which inhabits damp forest soils.

6.3. Order: Hypnales. The inner peristome is highly differentiated. Long setae typically terminate in inclined capsules. Brachythecium, Hypnum, Hylocomium (Fig. 11.126, Q), Pleurozium, and Plagiothecium include numerous species frequently found on forest soil; the genus Cratoneuron (R) comprises important tufa-forming mosses.

The systematic position of the following orders remains unclear.

7. Order: Buxbaumiales¹. The protonema is long-lived and rich in chlorophyll, largely providing nutrition for both the gametophyte² and the sporophyte. In Buxbaumia, the highly reduced gametophyte³ (exhibiting sexual dimorphism; see Fig. 11.116, A–C) contributes very little to the nutrition of the physiologically independent sporophyte, which is equipped with abundant assimilatory tissue. In Diphyscium (D), the seta-less capsule sits within a rosette of green leaves.

¹ This and the following order should most likely be assigned to separate classes. — Ed. note.

² The protonema represents a developmental stage of the gametophyte rather than a separate plant or generation. — Ed. note.

³ Actually, a gametophore. — Ed. note.

8. Order: Tetraphidales. The four peristome teeth each consist of several longitudinal cell rows. Tetraphis pellucida (see Fig. 11.126, M–O) is frequently found on decaying wood.

9. Order: Schistostegales. The sole species of this order is the "luminous moss" Schistostega pennata (see Fig. 11.125). It is distinguished by secondarily distichous leaves, the absence of a peristome, and a persistent protonema that reproduces via multicellular gemmae. The protonema grows in rock crevices and soil depressions. It forms spherical cells that capture incident light and partially reflect it (E, H). The gametophyte leaves are initially attached obliquely in a spiral arrangement, but during development, they assume a vertical position perpendicular to the incoming light rays (A, B).

4. Class: Hornworts (Anthocerotopsida)

The gametophytes of hornworts are thalloid, yet they differ from the previously discussed liverworts (Classes 1 and 2) in several key features. The gametophyte cells lack oil bodies (which are common in liverworts) and contain only a single chloroplast with a pyrenoid. The gametophyte possesses true stomata (whereas the liverwort Marchantia bears only air pores). The sporophytes grow via an intercalary meristem, resulting in indeterminate growth. The method of sporophyte attachment to the gametophyte (transfer tissue) is similar to that observed in Psilotopsida among fern allies, but is unknown in any other bryophytes. The capsule also features stomata and dehisces by two valves. The elaters of hornworts differ in their origin and appearance from those of liverworts (true mosses lack elaters entirely).

Antheridia originate endogenously from the very beginning (in liverworts they are initially exogenic, though they may later become engulfed by gametophytic tissue); archegonia are likewise embedded within the thallus.

Hornworts comprise a small group of about 100 species, which are united into a single surviving order.

Order: Anthocerotales. The gametophyte is a discoid, lobed, very simply structured thallus a few centimeters in length, attached to the soil by rhizoids (Fig. 11.127, A). Unlike all other bryophytes, the cells of the relatively uniform parenchyma contain only a single large saucer-shaped chloroplast with a pyrenoid¹. The epidermis of the lower thallus surface bears stomata with two Kidney-shaped guard cells. The substomatal chamber located beneath is filled with mucilage and is frequently colonized by the cyanobacterium Nostoc (B). Leaves, ventral scales on the lower thallus surface, and cellular oil bodies are all absent. The rhizoids are smooth-walled.

¹ In some species, cells contain multiple chloroplasts. — Ed. note.

Fig. 11.127. Anthocerotopsida, Anthocerotales:

A — Phaeoceros laevis, thallus with young and dehisced sporogonia (2×); B — Anthoceros vincentianus, stoma on the lower thallus surface, with the substomatal chamber colonized by Nostoc (270×); C — Anthoceros punctatus, longitudinal section of a young sporogonium (130×); D — Dendroceros crispus, longitudinal section of a nearly mature sporogonium (80×); E — Anthoceros punctatus, unequal cell divisions in the archesporium (100×); F — Anthoceros husnoti, transverse section of a sporogonium showing spore tetrads and columella; arrows indicate sites of sporogonium wall rupture (100×); G — Anthoceros pearsoni, sporogonium stoma (125×); a — archesporium; c — columella; e — elaters; f — sporogonium haustorium; s — spores; sm — spore mother cells; w — capsule wall.

Antheridia and archegonia are embedded in the thallus on its dorsal side. The fertilized egg cell divides by a transverse wall into two cells, of which

the upper cell (i.e., the one facing the archegonial neck) develops into the sporogonium following further divisions, while the lower cell forms a thicker haustorium that penetrates the thallus via rhizoid-like cells (Fig. 11.127, D)¹.

¹ Contrasting the sporogonium and the haustorium is incorrect, as the haustorium is an organ of the sporogonium itself. — Ed. note.

The sporogonium is a seta-less, pod-like capsule² ranging from one to several centimeters in length, which dehisces into two longitudinal valves much like a legume pod (Fig. 11.127, A). Unlike the capsules of Marchantiopsida, it is characterized by complex tissue differentiation. Running along the axis of the capsule is a sterile columella (C, D: c) composed of several cell rows. The columella is surrounded by a thin layer of sporogenous cells (archesporium, a) which, In addition to meiospores, also produce sterile cells known as elaters. The diploid spore mother cells and the cells that develop into elaters are sister cells; for each spore mother cell (and consequently each spore tetrad resulting from meiosis), there is either one mature elater or a still-dividing sterile cell whose successive mitotic divisions can multiply the final number of elaters significantly. The elaters are oriented perpendicularly to the axis of the sporogonium (E).

² Sporogonium = capsule + intercalary meristem zone + haustorium. — Ed. note.

Unlike all other bryophytes, the sporophyte capsule does not mature all at once; instead, it undergoes prolonged elongation driven by a meristematic zone located at the base of the capsule. The sporogonium wall contains two-celled stomata (Fig. 11.127, G) and also possesses chloroplasts within its cells.

Representatives of the family Anthocerotaceae produce sporogonia 1–7 cm long on the thallus. Two genera are found in Germany: Anthoceros (e.g., A. punctatus), which features mucilage cavities visible as dots on the upper surface of the dissected thallus, accompanied by dark, densely spinose spores; and Phaeoceros (e.g., Ph. laevis, found on lime-deficient stubble fields), which lacks mucilage cavities in its lobed thallus and produces yellowish, papillate spores. The thallus of Notothyladaceae is extremely small by comparison (a few millimeters in diameter).

Paleontological evidence regarding the evolution of Anthocerotopsida is unfortunately entirely absent. Unlike liverworts and similarly to true mosses, hornworts possess true stomata. This trait links true mosses and hornworts with higher land plants. According to DNA sequence analyses, hornworts appear to be more closely related to the subsequent groups of green land plants than to other bryophyte lineages.

Occurrence and Life Habits of Bryophytes

Mosses conquered the land and populated it with numerous species. Their adaptations to terrestrial life are highly diverse: for example, significant tolerance to desiccation (poikilohydric plants, see 6.10.3.6), reduced or regulated transpiration (in particular, due to the cuticle; sterile walls of gametangia and sporogonia; stomata; growth in dense cushions and turfs), their adaptations for the absorption, accumulation, and conduction of water, and the development of various growth forms suited to terrestrial habitats (for example, dendroid — see Fig. 11.126, P, foliar — Q, pendulous — S, felt-like, crustose — R, cushion-like — H, turf-forming), which ensure the colonization of favorable niches and adaptation to extreme environmental conditions.

The strength of moss tissues is provided by the swelling of cell walls rather than turgor, as in higher vascular plants. Therefore, dried mosses regain their original appearance when placed in water. With few exceptions, water absorption and loss occur across the entire surface. The capillary system between the stem, rhizoids, and leaves (if present) ensures significant water accumulation, which is enhanced in some leafy liverworts by the development of "water sacs" (see Fig. 11.114, 1), an imbricate (incubous or succubous — see Jungermanniopsida) leaf arrangement, and the presence of underleaves and lobes (see Fig. 11.114, F, H, D), and in mosses, by growth in dense, tall turfs. Marchantia, Sphagnum, and Leucobryum also accumulate water in hyaline cells (see Fig. 11.110; 11.120, G; 11.121). The columella in the capsule of mosses serves as a reservoir of nutrients and water for the developing spores. In certain mosses (for example, Funaria, Encalypta), water accumulation is facilitated by an inflated calyptra. It is primarily this ability of mosses to retain significant amounts of water that accounts for the buffering effect of forests on the landscape water balance. The water saturation of raised bogs is due to precipitation and the immense water-holding capacity of peat mosses (various Sphagnum species).

The aforementioned capillary system also serves as an external water conduction system, which is predominant in mosses. Mosses with a central strand (which include most acrocarpous mosses and a few liverworts) conduct water absorbed by rhizoids through hydroids. This internal conducting system is particularly well-developed in Polytrichanae, which even possess true leaf trace bundles connected to the central strand, ensuring the water supply to the leaves (closed conducting system).

Dispersal of spermatozoa and spores. While fertilization of the egg by spermatozoa requires liquid water, spores are dispersed by the wind. Their release is facilitated by changes in humidity and specialized dispersal mechanisms (for example, elaters; capsule dehiscence mechanisms; see 8.4). The umbrella-like, brightly colored apophysis in the sporogonia of Splachnum species (see Fig. 11.126, K) promotes the dispersal of clumped spores by insects¹.

¹ A significant role in attracting insects is also played by the odor emitted through the stomata on the apophysis. — Editor's note.

Some species have well-developed photosynthetic organs. The thallus of Marchantia already resembles the leaf of vascular plants in its Anatomical Structure, including adaptations for gas exchange, though these are less efficient and structurally different. On the upper side of Polytrichum leaves, freely rising lamellae are formed to absorb light for photosynthesis. Where true stomata occur (in hornworts on the gametophyte thalli and on the sporophytes, and in mosses on the sporophytes), they are often secondarily non-functional. As in some extant mosses, stomata originally served to facilitate gas exchange and water transport (via transpiration). Most often they are located in the plane of the epidermis, but in some species they are deeply sunken.

The distribution ranges of mosses largely coincide in character with those of flowering plants. The distribution of some species now found worldwide (Marchantia polymorpha, Bryum argenteum, Funaria hygrometrica), may have been influenced by humans. In plant communities dominated by flowering plants, mosses form their own subordinate communities (synusiae, see 14.3.4), often competing with lichens. They form their own formations only in the Arctic (tundra) and sometimes on raised bogs, where the productivity of the continuous moss cover reaches its maximum values: 200 – 900 g of dry matter per 1 m² per year; this corresponds to the hay yield of a medium-quality meadow.

Mosses are most common as hygrophytes in high-humidity areas: in forests and bogs. In general, liverworts are more moisture-loving than mosses. Mosses are usually less affected by extreme conditions, such as severe dryness, high temperatures, and intense radiation, and can tolerate lower light intensities than flowering plants. Therefore, they penetrate deep into crevices and caves, and can also grow successfully on forest soils and in other shaded places, especially in the form of mats, turfs, and crusts. Mosses reach their greatest diversity of forms, including pendulous forms up to a meter long (see Fig. 11.126, S) and epiphytes, in the tropics, particularly in cloud and montane forests. They have developed a wide variety of adaptations for capillary water retention. A surprisingly large number of moss species colonize the leaf surfaces of other plants. Such epiphyllous mosses are currently viewed not strictly as epiphytes, but sometimes as hemiparasites, which penetrate beneath the cuticle of the host leaf with their rhizoids to extract water and salts.

Mosses of the temperate zone (except for epiphytes, as well as mosses on soil and stony substrates) often exhibit rhythmic growth patterns clearly linked to the seasons (see Fig. 11.126, B, Q). They are rarely annuals, but more commonly green throughout the year (evergreen) and, like leafy liverworts, retain their leaves in winter.

Xerophytic mosses possess high desiccation tolerance as well as resistance to high temperatures and can remain in an air-dry state for a long time (Tortula muralis up to 14 years) without losing viability. Spores, by contrast, are much less resilient. Growing in direct sunlight and therefore frequently experiencing drought, mosses often grow in low, dense turfs and tight cushions (see Fig. 11.126, H). They often have a silvery-gray color due to long, dead leaf tips. Such 'glassy hairs' (G) probably serve for protection against excess light and to reduce transpiration. The broad, single-layered leaf margins in Polytrichum piliferum can fold over the multilayered middle portion that bears the photosynthetic lamellae, thereby protecting it from drying out (like rolling leaves, see 4.3.3.2). Mosses can withstand extreme temperatures: they can be found, on the one hand, on rocks in the nival zone of high mountains, as well as in the Arctic and Antarctic, and on the other hand, in open areas where soil temperatures can reach 70 °C. In experiments, some air-dried mosses survived heating to 110 °C for 30 min while remaining alive.

Several species have secondarily adapted to aquatic life (hydrophytes), with both external and internal water conduction systems being lost.

Fontinalis antipyretica and other aquatic mosses are highly sensitive to prolonged periods out of water. Mosses living in lime-rich streams and waterfalls (for example, Eucladium verticillatum, Bryum pseudotriquetrum, Cratoneuron commutatum), along with various species of cyanobacteria (Oocardium) and Chara, make a significant contribution to the formation of calcareous tufa. By extracting carbon dioxide from the water, they convert dissolved bicarbonate into poorly soluble calcium carbonate, which precipitates.

A few mosses (for example, Pottia species) grow as halophytes along seacoasts and in inland saline areas.

In the thallus cavities of Blasia (see Fig. 11.114, C) and Anthoceros (see Fig. 11.127, B), the blue-green alga Nostoc lives as a symbiont. The rhizoids or cells of the thallus or stem of many liverworts contain fungal hyphae; however, in each individual case, it is difficult to determine whether this represents parasitism or a mycorrhiza-like Symbiosis (see 9.3.1). The chlorophyll-free liverwort Cryptothallus mirabilis, which lives beneath mats of mosses, feeds as a parasite on fungal hyphae, whereas the rhizoids of Marchantia and other mosses may, conversely, be infected by parasitic fungi.

Overview of Bryophytes. The Relationship of bryophytes and the vascular plants discussed below to preceding Chlorobionta is indicated by many shared characteristics, including the same photosynthetic pigments, starch formation in plastids, the presence of cellulose in cell walls, and a similar structure of motile reproductive cells. Mosses probably evolved from ancestors corresponding to streptophytes within the Chlorobionta. Among these, mosses are closer to the stoneworts (Charophyceae) due to their biflagellate asymmetric spermatozoa and a number of different ultrastructural and biochemical features, and possibly to Klebsormidiophyceae, than to other green algae. The protonemata of mosses, which in some forms can directly develop gametangia¹ and are filamentous in many, indicate the transition that occurred from a filamentous to a parenchymatous thallus.

¹ Gametangia develop on gametophores, even if they are highly reduced. — Editor's note.

The evolutionary development of bryophytes probably proceeded from the Silurian-Devonian boundary in parallel with the Evolution of the first terrestrial pteridophytes. The phylogenetic relationships of hornworts remain unclear; they likely evolved in parallel with liverworts and mosses. Whether they are indeed the closest relatives (among bryophytes) to higher vascular plants remains controversial. The ancestral forms of bryophytes, like vascular plants, apparently inherited conducting structures for water and assimilates from common ancestors. This is supported by the high degree of similarity in Structure and function between the hydroids and leptoids of mosses and the tracheids (vessels) and sieve cells of pteridophytes, as well as the presence of archegonia and stomata in both groups. During the evolution of bryophytes, the gametophyte (the green moss plant) and possibly the sporophyte underwent various simplifications, but simultaneously achieved biological progress (progressive reduction). Thus, among mosses, erect, tall acrocarpous forms with a well-developed conducting system resembling a protostele (Polytrichanae) are considered ancestral to prostrate, branched pleurocarpous species lacking a conducting system and a leaf costa. The presence of non-functional stomata can also be interpreted as a result of regression. In contrast, progressive development occurred in the cellular network of leaves (from parenchymatous to prosenchymatous) and the structure of the capsule mouth (peristome).

Individual fossil bryophytes are found from the Upper Devonian; they provide little information for understanding their origin. Sporogonites from the Devonian, however, can be considered a doubtful link between bryophytes and the closely related pteridophytes (Psilophytopsida). Thalloid and leafy liverworts, as well as the first mosses (Muscites), are found in the Carboniferous of England. This indicates the great evolutionary age of bryophytes. Mosses that can be assigned to Sphagnidae and Bryidae have been described from the Permian of Russia (Pechora, Kuznetsk). Mosses of the Lower Carboniferous and Permian had leaf costae (including Protosphagnales), whereas the first forms without costae are known only from the Triassic and became increasingly common in the Late Jurassic. Most fossil moss discoveries, with an increasing proportion of pleurocarpous forms, are known from the Tertiary period. They can be assigned to modern genera.