Brown algae is the largest type of algae. Brown algae is in the phylum Phaeophyta, which means "dusky plants." Brown algae is brown or yellow-brown in color and found in temperate or arctic waters. Brown algae typically have a root-like structure called a "holdfast" to anchor the algae to a surface.
Examples of brown algae: kelp, rockweed (Fucus), Sargassum.
There are more than 6,000 species of red algae. Red algae has its often brilliant color due to the pigment phycoerythrin. This algae can live at greater depths than brown and green algae because it absorbs blue light. Coralline algae, a group of red algae, is important in the formation of coral reefs.
Example of red algae: Irish moss, coralline algae, dulse (Palmaria palmata).
There are more than 4,000 species of green algae. Green algae may be found in marine or freshwater habitats, and some even thrive in moist soil. These algae come in 3 forms: unicellular, colonial or multicellular.
Examples of green algae: sea lettuce (Ulva sp.), which is commonly found in tide pools, Codium sp., one species of which is commonly called "dead man's fingers."