BOTANY WITH THE BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

IX. VASCULAR SPORE PLANTS

Subclass Peat Mosses (Sphagnidae)

The subclass includes a single order, Sphagnales, a single family, Sphagnaceae, a single genus, Sphagnum, and about 300 species.

Peat mosses grow mainly in oligotrophic woodland bogs, where they form cushion-like turfs. The gametophytes lack rhizoids and possess an upright stem that gradually dies off from the base, bearing leaves—phyllids—along the stem and on lateral branches. These leaves are nerveless and consist of a single Cell layer made up of two cell types: narrow, living, green chlorophyllous Cells, and dead, colourless, hyaline (Water-storing) cells filled with air or water.

The stem is covered with a multi-layered epidermis (hyalodermis), whose spiral cells feature thickenings and pores that facilitate water conduction. Deeper within lie prosenchymatous cells with thickened walls that provide structural strength to the stem. The stem center is occupied by a robust core formed of large-celled parenchyma. Due to these structural features, Sphagnum can absorb and retain up to 30 times its dry weight in water. Air bubbles trapped within the cells of Sphagnum leaves impart a pale colour to the plants, which is why they are commonly known as white mosses. Stem leaves range from triangular to spathulate, while branch leaves vary from ovate to linear.

Sphagnum gametophytes are monoecious or dioecious. Antheridial branches are club-shaped and swollen at the tips, often brightly coloured, and situated near the apex of the stem. Antheridia occur singly in the axils of perichaetial leaves. Archegonia, and subsequently sporogonia, are located singly at the apices of shortened lateral branches. They comprise capsules, pseudopodia, and haustoria. The sporogonium capsule is spherical and opens with a small lid. The sporangium is positioned above the dome-shaped columella. The capsule lacks a peristome. The spore germinates into a plate-like protonema.

Sphagnum can reproduce vegetatively (via body fragments, especially branches).

About thirty species of peat mosses grow in Ukraine. The best-known Sphagnum species include: Sphagnum cuspidatum, S. centrale, S. compactum, S. fallax, S. fuscum, S. fimbriatum, S. nemoreum, S. obtusum, S. palustre, and S. magellanicum (Figs. 93, 94).

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Fig. 93. Sphagnum palustre

Fig. 94. Sphagnum nemoreum

Sphagnum nemoreum is represented by monoecious and dioecious gametophytes forming tall, dense, red or purple, often mottled, less frequently greenish or brownish-green cushion-like turfs. Branches occur in clusters of 3 to 5. Branch leaves are up to 2 mm long, ovate-lanceolate with appressed tips. Stem leaves are triangular-ligulate or triangular. The plants sporulate in late summer. They are widespread in damp and boggy coniferous forests, on waterlogged clear-cuts, as well as in fens and raised bogs.

Sphagnum magellanicum is a dioecious plant forming large, tall and loose, or low and dense turfs of reddish or purple, occasionally greenish or yellow hues. There are up to 4 branches per cluster. Branch heads are Kidney-shaped. Branch leaves are up to 2.5 mm long, broadly ovate, strongly concave, with a rounded apex. Stem leaves are up to 2 mm long, oblong-ligulate or ligulate-spathulate, widening upwards. They sporulate in late summer and occur in raised bogs within pine forests.

The dead remains of peat mosses accumulate at the bottom of water bodies or bogs, forming peat under anaerobic conditions. Approximately 1 mm of peat is deposited annually. It contains a high proportion of carbon (up to 60%) and little ash (1–6%), making it a valuable fuel and organic fertilizer. Sphagnum possesses high hygroscopicity and antiseptic properties, largely due to the presence of a phenolic substance known as sphagnol. Dry Sphagnum is used as animal bedding, thermal insulation in residential and outbuildings, and as a growing substrate for ornamental plants.

Certain Sphagnum species (S. apiculatum, S. contortum, S. platyphylum, S. riparium) are consumed by animals (adult crustaceans and insects, as well as their larvae).