Green algae

The "green algae" is the most diverse group of algae, with more than 7000 species growing in a variety of habitats. The "green algae" is a paraphyletic group because it excludes the Plantae. Like the plants, the green algae contain two forms of chlorophyll, which they use to capture light energy to fuel the manufacture of sugars, but unlike plants they are primarily aquatic. Because they are aquatic and manufacture their own food, these organisms are called "algae," along with certain members of the Chromista, the Rhodophyta, and photosynthetic bacteria, even though they do not share a close relationship with any of these groups.

The above picture shows a dense growth of sea lettuce (Ulva), growing in a tide pool at the Berkeley Marina. This is a marine species of "green algae" often found attached to rocks, and exposed at low tide.

Over 5,000 species of green algae are known, mostly unicells or simple filaments from fresh water, but there are diverse green algae in tropical marine habitats. Like land plants, the greens store starch (amylose or amylopectin) and have chlorophyll a and b as well as secondary pigments : carotenes, lutein, zeaxanthin. (Some Chlorophyta also have siphonoxanthin.) The chloroplast endoplasmic reticulum is absent in green algae, and t heir cell walls are often composed of cellulose, hydroxproline, glycosides, xylans, mannans or sometimes calcium carbonate.