noun, plural: green algae
Any of the photosynthetic algae that includes the chlorophytes and the charophytes, which are characterized by containing the pigments chlorophyll a and chlorophyll b and storing food as starch within plastids
Algae are aquatic, photosynthetic, eukaryotic organisms ranging from unicellular to multicellular forms, and generally possess chlorophyll but lack true roots, stems and leaves characteristic of terrestrial plants. Green algae are a group of algae characterized by their greenish color as opposed to other groups of algae such as red algae (Rhodophyta), brown algae (Phaeophyta), golden algae (Chrysophyta), yellow-green algae (Xanthophyta), blue-green algae (Cyanophyta), diatoms, dinoflagellates, etc. The greenish color and photosynthetic capability of the green algae are associated with the presence of chlorophylls a and b in their plastids. These pigments are in the same proportions the same way as those in higher plants. Other pigments are also present, though, such as beta carotene and xanthophylls.
Green algae have many forms: unicellular, multicellular, or colonial. Unicellular green algae are solitary, single-celled photosynthetic organisms (e.g. Micrasterias sp.). Multicellular forms are those that appear filamentous or forming leaf-like thalluses (Ulva sp.). Some of them form colonies, such as Volvox species.
Green algae include the charophytes and the chlorophytes. The charophytes are green algae mainly found in freshwater whereas the chlorophytes are those found mostly in marine water. There are also green algae that live on terrestrial habitats (e.g. soil, rocks, and trees). Certain green algal species have been found to form symbiosis. For instance, Chlorella species form symbiosis with Hydra species.