Green Algae
Green Algae, members of the largest phylum of the algae, numbering some 6000 to 7000 species. They are commonly known as green or grass-green algae because of their bright green color, which is imparted by two chlorophylls, a and b. Among the oldest of all organisms—the first green algae appeared more than 2 billion years ago in the fossil record—they are believed to be the most immediate relatives of the green land plants.
Green algae may occur as single cells (which may be either motile or nonmotile), in colonies (more often nonmotile), and as multicellular filaments (nonmotile). Most have cell walls made up of two layers: an inner cellulose layer, and an outer layer of pectin. The unicellular forms assume a virtually endless variety of shapes; colonial forms may be loose aggregates of single cells or may have these cells arranged in a characteristic pattern. Some filamentous types bear a superficial resemblance to higher plants. The motile unicellular organisms are free-swimming, moving by means of whiplike flagella (usually two in number). Even the nonmotile species may produce motile reproductive cells (zoospores).
Scientific classification: Green algae make up the phylum Chlorophyta. The oldest green algae are classified in the genus Gunflintia.
Green algae may occur as single cells (which may be either motile or nonmotile), in colonies (more often nonmotile), and as multicellular filaments (nonmotile). Most have cell walls made up of two layers: an inner cellulose layer, and an outer layer of pectin. The unicellular forms assume a virtually endless variety of shapes; colonial forms may be loose aggregates of single cells or may have these cells arranged in a characteristic pattern. Some filamentous types bear a superficial resemblance to higher plants. The motile unicellular organisms are free-swimming, moving by means of whiplike flagella (usually two in number). Even the nonmotile species may produce motile reproductive cells (zoospores).
Scientific classification: Green algae make up the phylum Chlorophyta. The oldest green algae are classified in the genus Gunflintia.
