Chromalveolata

Chromalveolata was a proposed eukaryotic supergroup introduced in the early 2000s to organize several major lineages that were thought to share a common origin of their plastids. The hypothesis, associated with Thomas Cavalier-Smith, grouped Alveolata and Stramenopiles (also called Heterokonts) and, in some versions, cryptophytes and haptophytes, on the basis of molecular data and the idea that their plastids originated from a secondary endosymbiotic event with a red alga.

Members of the proposed assemblage include a wide range of organisms. Alveolata comprises ciliates, dinoflagellates, and apicomplexans. Stramenopiles include diatoms, brown algae, and oomycetes. Many members are photosynthetic, but several lineages within the group are nonphotosynthetic or parasitic. The shared feature cited for Chromalveolata was the retention or remnants of plastids derived from red algae, a consequence of a hypothesized single endosymbiotic event.

Current understanding has shifted. Molecular phylogenetic analyses increasingly support the SAR grouping, in which Stramenopiles and Alveolates are related, but do not recognize Chromalveolata as a monophyletic or coherent clade. As a result, Chromalveolata is largely considered obsolete or, at best, a deprecated heuristic rather than a robust taxonomic unit in contemporary classifications.

The idea of Chromalveolata contributed to debates on plastid evolution and eukaryotic diversification, but modern phylogeny favors more nuanced relationships among these major lineages within broader frameworks such as SAR.