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

VI. SYSTEM OF THE PLANT KINGDOM

LOWER SPORE PLANTS

GENERAL CHARACTERISTICS AND FEATURES

Division Red Algae - Rhodophyta

Predominantly marine, microscopic and macroscopic eukaryotic Algae comprising about 5,000 species that grow in the benthos or periphyton, often at considerable depths (20-40 m, and occasionally 100-200 m), and sometimes in the soil. Macrophytic forms feature a complex morphological and Anatomical Structure. In freshwaters, they are rare and mostly microscopic—either coccoid or filamentous forms. Known since the Cambrian period (early Paleozoic, about 600 million years ago), they unite unicellular, colonial, and multicellular algae with coccoid, filamentous, heterotrichous, pseudoparenchymatous, and parenchymatous thallus structures, being either uninucleate or multinucleate.

Most of them are characterized by a pseudoparenchymatous type of structure formed by the interweaving of lateral "branches" (assimilatory filaments) of a monoaxial or multiaxial thallus. Lamellar thalli occur only rarely.

Red algae are distinguished by a complex set of Photosynthetic Pigments: chlorophyll a and phycobilin pigments (phycocyanin, allophycocyanin, and phycoerythrin), as well as carotenoids such as α- and β-carotenes, cryptoxanthin, taraxanthin, zeaxanthin, and lutein.

Depending on the quantitative characteristics and The ratio of specific pigments, the coloration of the red algal thallus varies greatly: from crimson-red (dominance of phycoerythrin) to gray, steel-gray, or blue-green (dominance of phycocyanin), etc. The assimilation product is floridean starch (a polysaccharide), and occasionally Glycogen, which are deposited in the Cytoplasm outside the METABOLISM/14.html">Chloroplasts.

A characteristic feature of red algae is the complete absence of flagellated stages and centrioles in their life cycle.

The Cells of red algae are typically eukaryotic, possessing a three-layered pectin and Cellulose-pectin Cell wall. The Cell wall contains phycocolloids (Agar and agaroids) and is frequently encrusted with calcium carbonate. Adjacent cells are interconnected by plasmodesmata passing through Primary and secondary pits. The presence of pore canals between cells is a unique feature of red algae, and the type of plugging structures (pit plugs) closing them serves as a diagnostic feature at the order level. Chloroplasts are parietal, numerous, lamellar or discoid, granular, or more rarely central and stellate; they are surrounded by a double-membrane envelope, contain single thylakoids, and are of primary endosymbiotic origin. Cells are uni- or multinucleate, and mitosis is closed.

Reproduction in red algae occurs sexually (via a specific type of oogamy where both male and female Gametes are non-motile) and asexually (via haploid spores: monospores and tetraspores), as well as vegetatively (by Cell Division, fragmentation of multicellular thalli, and adventitious "shoots").

The Sexual process in red algae is oogamous, yet it proceeds with A number of specific features leading to The formation of yet another category of spores—carpospores, which are grouped into a structure known as a cystocarp. The male sex Organs (spermatangia) produce a single non-flagellated spermatium each, while the female sex organs (carpogonia) produce a single egg cell each. Antheridia are represented by small cells clustered in bunches at the ends of branchlets. Oogonia (carpogonia) have a distinct flask-like shape with a narrowed neck-like upper portion (trichogyne) and an expanded lower portion containing cytoplasm and a nucleus (the venter). Spermatia are released from spermatangia, passively transported by Water currents, and, upon reaching a carpogonium, fertilize the egg cell. Immediately after Fertilization, the zygote develops without a resting period into a unique generation present only in red algae—the carposporophyte. The carposporophyte forms carpospores (either directly from the venter or with the participation of ooblastema filaments and auxiliary cells), which give rise to a new sporophyte.

In some representatives, auxiliary cells are located near the carpogonium and form a so-called procarp with it; following the fusion of the auxiliary cell contents with the venter of the fertilized carpogonium, gonimoblasts bearing carpospores are formed. Carposporangia that are tightly grouped and covered by an envelope developing from cells adjacent to the carpogonium are called cystocarps. The formation of carpospores follows three different pathways, which determine the three main structural types of the carposporophyte.

The life cycle of red algae is predominantly haplo-diplophasic, involving reduction division at sporogenesis and the alternation of three generations: the gametophyte, carposporophyte, and sporophyte, featuring a successive or non-successive alternation of Selection/8.html">Asexual and sexual generations.

Red algae play a significant role in various sectors of the national economy, including the food, confectionery, medical, and microbiological industries. They are an essential component of hydrobiocenoses—especially in marine ecosystems of the Earth's southern regions—serving as a food base for numerous aquatic organisms, acting as lime-accumulating agents, bio-indicators for water quality assessment, and bio-organic fertilizers. Red algae produce phycocolloids (agar, agaroids, carrageenan)—gel-forming substances that are indispensable not only for food preparation but also in textile and leather manufacturing, pharmaceutical developments, and scientific laboratory research (as components of chromatographic and electrophoretic plates, solid culture media, etc.). The main producers of agaroid products are natural stocks of species belonging to the genera *Ahnfeltia*, *Chondrus*, *Gracilaria*, *Gelidium*, and *Phyllophora*, as well as aquaculture species such as *Eucheuma* and *Porphyra*. Medical Applications have been found in species of the genera *Corallina*, *Digenia*, *Lithothamnion*, and *Ptilota*, while *Porphyra* and *Rhodymenia* serve as food components (red sea lettuces).

Ukraine features a unique marine reserve, Zernov's Phyllophora Field, which concentrates substantial reserves of *Phyllophora* species and was actively exploited until the 1970s.

The systematics of the division is based on morphological and Anatomical Features (The structure of the carpogonium and chloroplasts, the mode of asexual reproduction, assimilation products, and the presence of secondary pits) and involves division into two classes: Bangiophyceae and Florideophyceae. However, modern molecular genetic studies do not fully support this Classification, requiring further research. We consider the division of the Rhodophyta in its traditional sense and provide a brief description of only some Representatives of the flora of Ukraine.