Green Algae (Division Chlorophyta)
These plants occur widely wherever there is water. Many are found in moist soil and on tree trunks and even in ice. Chlorophytes range in size from microscopic cells and filaments to large colonies several feet long and quite broad.
This group typically contains chlorophyll A and chlorophyll B together with various carotenoid and xanthophyll pigments contained in chloroplasts.
Some green algae may not appear green due to the masking of chlorophyll by one or more of the accessory pigments. Manufactured food is stored principally as starch, also cellulose is present in the cell walls.
The green algae are especially common in a variety of body forms. Single celled forms such as chlorella are sometimes common in lakes and ponds, often in numbers sufficient to color the water.
Desmids are green algae which occur as single cells or sometimes as small colonies in filamentous and filaments of minute cells. These often exhibit intricately beautiful patterns of body form. Desmids may be found on objects in the lake or freely floating as important constituents of phytoplankton. Cosmarium and Closterium are common forms in lake or pond plankton.
Colonial green algae such as Volvox and Eudorina are common in lakes and ponds. The thalus or body of other green algae may appear as a continuous filament or as a partitioned or septate branching filament. The species of Ulothrix and Spirogyra are unbranched filamentatious forms. The filament of each plant is a very small, threadlike structure attached to the substrate by a specialized cell called a holdfast.
Except for the holdfast cell, all the cells of the filament are identical and are arranged end to end in a single series. Each cell contains a single nucleus and a single large chloroplast.
Other attached green algae use rizoid like structures at the bases of filaments which trail out as tassels into the current. In many of the filamentatious Chlorophychae, in some genera Cladophora Oedogonium and Ulothrix tassels may become very long and in some cases may exceed a meter in length.
Stonewarts of which Chara is an example are often placed in the Chlorophyta. These large algae possess whirls of branches along a stemlike filament and holdfast to anchor the plants in the substrate. The common name derived from the brittle, stony texture of the algae caused by deposits of lime frequently found on the plant surface in highly calcareous streams or lakes. Nitella, similar in form to Chara, often thrives in soft or acidic waters. Under such conditions, Nitella lacks the hard texture.