Classification of Cladophorales | Algae

In this article we will discuss about the classification of cladophorales.

Family Cladophoraceae:

This family contains many fresh-water forms. Some of the large genera, such as Cladophora, have both fresh-water and marine representatives, but there are several strictly marine genera. The plants are composed of multinucleate cells arranged in uniseriate fashion in simple or branched filaments.

The chloroplast is parietal and reticulate. The filaments are usually attached by rhizoids. Generic separations have traditionally been made on vegetative characters such as the presence or absence of branches, the kind of branches, and the form of the basal cell and its attachment rhizoids.

Genus Cladophora:

Both fresh-water and marine species are quite common, growing abundantly in shallow water which may be stagnant or running. They inhabit mainly being attach­ed to rocks and other objects under water including submerged water plants and Mollusca shells by fairly long rhizoidal branches. Filaments are typically branched with numerous cross-walls separating the coenocytic segments.

Growth in length of the different branches is practically restricted to the apical cell of the filament. Branches nearly always arise just beneath a septum resulting the appearance of dichotomy or trichotomy (Fig. 45A). Elongated cells with thick and distinctly stratified walls, discoid chloroplasts too. Internal to the chloroplast or chloroplasts as the case may be, usually numerous nuclei are embedded (Fig. 45D).

The perennial species of Cladophora are provided with a method of tiding over the unfavourable period of growth. The rhizoidal branches of the filaments undergo repeated divisions producing short branched filaments, the cells of which are filled with food material. These cells survive after the main parts of the filaments are dead and grow into new filaments in the next season.

In some of the fresh-water species certain cells of the filament may become swollen to form akinetes which develop into new branches.

Asexual reproduction is accomplished by the production of numerous small, pear- shaped, diploid quadriflagellate zoospores (Fig. 45F). The zoospores arise by simulta­neous division of the cell contents into numerous parts.

Normally zoospore formation is confined to the finer branches (Fig. 45E) and takes place in basipetal succession, but there are cases where zoospores may be formed from any cell except the basal rhizoidal cell. The zoospores germinate directly into new diploid filaments.

The gametes are biflagellate and their formation takes place like the zoospores (Fig. 45G). The fusing gametes are of same size and thus the process of sexual repro­duction is isogamous. The gametes from two different filaments fuse in pairs. Hence Cladophora is heterothallic.

The zygote germinates directly into a diploid filament immediately after formation without undergoing any resting period or meiosis. The resulting diploid filament is known—as the sporophyte and resembles the haploid gamete producing filament—the gametophyte. The diploid plant developing from the diploid zygote produces haploid biflagellate zoospores as a result of meiotic division.

These zoospores germinate to form haploid filaments which resemble the diploid filaments morphologically. Hence morphologically identical haploid and diploid filaments alternate with each other to complete the life cycle indicating a distinct alternation of generations which is again known as isomorphic or homologous alternation of generations (Fig. 46), the difference being in cytologica’ details.

Cladophora glomerata, a fresh-water species presents a wholly different type of life cycle. This difference may be compared with the various cycle found for Ectocarpus siliculosus under different conditions. In C. glomerata gametes and zoospores both are for­med on diploid filaments and meiosis takes place only during gamete formation so that there is no haploid generation. The diploid filaments propagate by a long succession of diploid zoospores. (Fig. 47).

A sexual diploid plant in which only the gametes are haploid is known as diplont.

Some Indian species of Cladophora:

Cladophora bengalensis Mart.; C. crispata (Roth.) Kutz.; C.furcata.; C. glomerata (L.) Kutz.; C. incurvata West et West; C. rottleri Kutz.; C. scitula (Suhr.) Kutz.

Special features of Cladophorales:

1. Filamentous branched plant body.

2. Cell wall is thick and stratified.

3. Cells multinucleate.

4. Asexual reproduction by diploid quadriflagellate zoospores.

5. Sexual reproduction by isogamy.

6. Exhibits isomorphic alternation of generations.