Algae ︎︎︎

Chlorophyta are commonly known as green algae and sometimes, loosely, as seaweed. They grow primarily in freshwater and saltwater, although some are found on land. They may be unicellular (one cell), multicellular (many cells), colonial (a loose aggregation of cells), or coenocytic (one large cell). Chlorophyta convert sunlight to starch that is stored in cells as a food reserve.

Green algae have dark- to light-green coloration that comes from having chlorophyll a and b, which they have in the same amounts as "higher plants"—the plants, including seed plants and ferns, that have well-developed vascular tissues that transport organic nutrients. Their color is determined by the amounts of other pigmentation, including beta-carotene (yellow) and xanthophylls (yellowish or brownish).

Like higher plants, they store their food mainly as starch, with some as fats or oils. In fact, green algae might have been the progenitors of the higher green plants, but that is the subject of debate.

Chlorophyta belong to the kingdom Plantae. Originally, Chlorophyta referred to a division within the Plantae kingdom comprising all green algae species. Later, green algae species living predominantly in seawater were classified as chlorophytes (i.e., belonging to Chlorophyta), while green algae species thriving mainly in freshwater were classified as charophytes (i.e., belonging to Charophyta).

The AlgaeBase database lists about 4,500 species of Chlorophyta, including 550 species of Trebouxiophyceae (mostly on land and in freshwater), 2,500 species of Chlorophyceae (mostly freshwater), 800 species of Bryopsidophyceae (seaweeds), 50 species of Dasycladophyceae (seaweeds), 400 species of Siphoncladophyceae (seaweeds), and 250 marine Ulvophyceae (seaweeds). Charophyta include 3,500 species allocated to five classes.

Jennifer Kennedy. Green Algae: Chlorophyta (ThoughtCo, 2019)