The Chromista are a eukaryotic supergroup, probably polyphyletic, 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 chloroplasts are surrounded by four membranes, and are believed to have been acquired from some red algae.
Chromista has been defined in different ways at different times. The name Chromista was first introduced by Cavalier-Smith in 1981; the earlier names Chromophyta, Chromobiota and Chromobionta correspond to roughly the same group.
It has been described as consisting of three different groups:
Chromophycées (Chadefaud, 1950)
The Chromophycées (Chadefaud, 1950), renamed Chromophycota (Chadefaud, 1960), included the current Ochrophyta (autotrophic Stramenopiles), Haptophyta (included in Chrysophyceae until Christensen, 1962), Cryptophyta, Dinophyta, Euglenophyceae and Choanoflagellida (included in Chrysophyceae until Hibberd, 1975).
Chromophyta (Christensen 1962, 1989)
The Chromophyta (Christensen 1962, 1989), defined as algae with chlorophyll c, included the current Ochrophyta (autotrophic Stramenopiles), Haptophyta, Cryptophyta, Dinophyta and Choanoflagellida. The Euglenophyceae were transferred to the Chlorophyta.
Chromophyta (Bourrelly, 1968)
The Chromophyta (Bourrelly, 1968) included the current Ochrophyta (autotrophic Stramenopiles), Haptophyta and Choanoflagellida. The Cryptophyceae and the Dinophyceae were part of Pyrrhophyta (= Dinophyta).
Chromista (Cavalier-Smith, 1981)
History and controversy
Molecular trees have had some difficulty resolving relationships between the different groups. All three may share a common ancestor with the alveolates (see chromalveolates), but there is evidence that suggests that the haptophytes and cryptomonads do not belong together with the heterokonts.
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