The Chromista are a paraphyletic eukaryotic supergroup, which may be treated as a separate kingdom or included among the Protista. They include all algae whose chloroplasts contain chlorophylls a and c, as well as various colorless forms that are closely related to them. These are surrounded by four membranes, and are believed to have been acquired from some red alga. There are three different groups:
The name Chromista was introduced by Cavalier-Smith in 1981; the earlier names chromophyte and chromobiont correspond to roughly the same group. Molecular trees have had some difficulty resolving relationships between the different groups. It now appears that all three share a common ancestor with the alveolates (see chromalveolates), but it is possible that the Chromista themselves are paraphyletic.
- T. Cavalier-Smith (1981). "Eukaryote kingdoms: seven or nine?". Biosystems. 14: 461–481.