Most chlorophytes are aquatic, but some green algae can live on the surface of snow, on tree trunks, in soils, or symbiotically with protozoans, hydras or lichen-forming fungi. Numbering about 8,000 species, the chlorophytes range in size from microscopic to quite large. The typical color of plants in the Chlorophyta, resulting from the dominant chlorophyll pigments, is some shade of apple or grass green, although certain species may appear yellow-green or blackish-green due to the presence of carotenoid pigments or high concentrations of chlorophyll. Chlorophytes appear more than a billion years ago in the fossil record.
Calcified green algae, particularly Halimeda spp., are especially important as major contributors of marine sediments. The sparkling white sand beaches of the Caribbean and many other areas in the world are largely the sun-bleached and eroded calcium-carbonate remains of green algae. The deepest occurring, fleshy, erect alga Johnson-sea-linkia profunda, (Littler et al., 1985)was found attached to bedrock at a depth of 157 meters off the Bahamas and is a member of this group.
Green algae have chlorophylls a and b and store starch as a food reserve inside their plastids. Most green algae have firm cell walls composed of cellulose along with other polysaccharides and proteins.