Algae

The actual term "algae" is not very useful in formal biology, because a number of disparate groups of unrelated organisms are aggregated under this broad term. The seven divisions of organisms that are considered within the algae are the Euglenophyta, Chrysophyta, Pyrrophyta, Chlorophyta, Rhodophyta, Paeophyta, and Xanthophyta. These divisions are separated on the basis of various features including their morphology and the biochemistry of their pigments, cell walls, and energy-storage compounds. The colors of these various algae types differ according to their particular mixtures of photosynthetic pigments, which typically include a combination of one or more chlorophylls and various accessory pigments. The latter can include carotenoids, xanthophylls, and phycobilins (these mask the green of the primary chlorophylls in various ways). The major differences among the seven divisions of algae are briefly summarized below.