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

VI. PLANT SYSTEMATICS

LOWER SPORE PLANTS

GENERAL CHARACTERISTICS AND FEATURES

Division Streptophyte Algae - Streptophyta

Eukaryotic, free-floating or attached, unicellular and multicellular, micro- and macroscopic (up to 30 cm), predominantly freshwater, less frequently brackish-Water and aerophilic Algae. They exhibit monad, coccoid, sarcinoid, filamentous, and heterotrichous types of thallus Structure, occasionally featuring parenchymatous-lamellar or articulated-annular thalli with leaf-like, stem-like, and rhizoid-like formations. This group of algae likely originated about 1,400 million years ago—in the Upper Precambrian-Proterozoic—and gave rise to vascular plants around 470 million years ago. Their current diversity comprises over 3,000 species, with about 900 species recorded in Ukraine. In terms of their pigment complex—chlorophyll a and b (in identical proportions), dominance over carotenoids (α-, β-, δ-, and ε-carotene), and presence of lutein-series xanthophylls (lutein, zeaxanthin, neoxanthin, violaxanthin, antheraxanthin)—they are analogous to green algae and higher plants. METABOLISM/14.html">Chloroplasts are primarily symbiotic, typically plant-like, enclosed in a double-membrane envelope, with thylakoids grouped into 2–6-member (sometimes more) lamellae or forming grana. The pyrenoid is embedded in the chloroplast stroma and penetrated by thylakoids. The reserve product is starch, which borders the pyrenoid as individual grains and is also located in the stroma. Reproduction occurs asexually (absent in highly organized forms).

Based on a combination of ultramicroscopic and molecular-biological traits, the independence of this plant group—which differs from green algae (Chlorophyta) and is classified under the division Streptophyta—has been confirmed. It encompasses both algae and vascular plants, representing an intermediate, phylogenetically related link in the overall plant evolutionary Lineage and containing the ancestral group of flowering plants. Diagnostic features of algae in this division include the presence of submicroscopic scales (on The Cell wall or flagella) in monad forms or their developmental stages, an asymmetric flagellar "ROOT" system with a multi-layered microfibrillar structure, The formation of a transverse cell plate between daughter Cells via a phragmoplast mechanism, as well as open or semi-closed mitosis.

Asexual reproduction occurs via biflagellate zoospores (with or without ultrastructural scales), aplanospores, or vegetatively through brood tubers (in charophyte algae). Sexual reproduction involves oogamy and conjugation (characteristic of only certain representatives). Cytokinesis is accomplished by a circular furrow (centripetal formation) or via the formation of a cell plate (centrifugal formation) of the phragmoplast type (initial cell plate microtubules orient perpendicularly to the future septum). The flagellar "root" system is characterized by an asymmetric arrangement, and the transition zone of the flagellum features a specific stellate structure.

The systematics of the division is currently undergoing development and refinement. The most widely recognized Classification scheme divides the algae of this division into 3 classes: Zygnematophyceae, Charophyceae, and Mesostigmatophyceae. These classes are differentiated based on the type of sexual process, ontogenetic features (presence of flagellar stages), cytokinesis and mitosis, The structure of reproductive Organs, and the flagellar apparatus. Furthermore, the division into orders is based on the morphological structure type of the algal thallus and its specific structural features.