Chromista
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The Chromista are a 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:
- Heterokonts or stramenopiles - brown algae, diatoms, water moulds, etc.
- Haptophytes
- Cryptomonads
However, these do not appear as close relatives in most molecular trees. Thus many biologists have been cautious in accepting the Chromista, and some argue the different groups acquired chloroplasts independently. The name Chromista was introduced by Cavalier-Smith in 1981; the earlier names chromophyte and chromobiont correspond to roughly the same group. Cavalier-Smith has suggested they share a common coloured ancestor with the alveolates, but this is also somewhat questionable.