greenalgae

Green algae are photosynthetic eukaryotes within the green plants (Viridiplantae). They comprise two major lineages: the Chlorophyta, mostly aquatic and unicellular or colonial, and the Streptophyta, which includes many multicellular forms and is the lineage that gave rise to land plants. Green algae are important primary producers in freshwater and marine ecosystems and are closely related to land plants.

They characteristically contain chlorophylls a and b, carotenoids, and store starch as a reserve carbohydrate. Cell walls are typically cellulose, and many species have chloroplasts with pyrenoids that concentrate carbon. Reproduction is diverse, including asexual division and sexual processes; life cycles range from haplontic to diplontic, with occasional alternation of generations.

Green algae inhabit oceans, rivers and lakes, damp soils, rocks, and tree surfaces, and they can form photobiont partnerships in lichens and other organisms. They are integral to aquatic food webs as primary producers, and some species form blooms or contribute to biofilms in various habitats.

Prominent examples include unicellular Chlamydomonas reinhardtii, colonial Volvox carteri, and multicellular Ulva (sea lettuce). Other well-known genera are Chlorella, Spirogyra, and Hydrodictyon. The group comprises thousands of species with a wide range of forms from simple filaments to sheet-like thalli.

Green algae are widely used as model organisms in research on photosynthesis and chloroplast evolution. They also have potential applications in biotechnology, such as biofuels, nutritional supplements, and bioremediation, though practical use depends on species-specific traits and ecological considerations.