Chromalveolata

Chromalveolata is a proposed eukaryotic supergroup comprising alveolates, stramenopiles, haptophytes, and cryptophytes. Its defining hypothesis is that their plastids descend from a red alga engulfed by a shared ancestor.

Secondary endosymbiosis: The origin of an organelle when a eukaryotic cell engulfs another eukaryote that already contains a primary organelle. The chromalveolate hypothesis proposes one red-algal endosymbiosis in the ancestors of its members.
Alveolata: A eukaryotic lineage characterized by flattened membrane-bound sacs beneath the cell surface. Alveolates form one of the four principal lineages included in Chromalveolata.
SAR supergroup: A major eukaryotic grouping comprising stramenopiles, alveolates, and Rhizaria. SAR retains two chromalveolate components but places them with Rhizaria and excludes haptophytes and cryptophytes.
Endosymbiotic gene transfer: The movement of genes from an endosymbiont's genome into the genome of its host. Transferred genes can obscure plastid origins and complicate tests of a common chromalveolate ancestor.
Red algae: A diverse lineage of photosynthetic eukaryotes that includes organisms with red pigments and red-algal plastids. A red alga is proposed to have supplied the plastid shared by chromalveolate ancestors.
Stramenopiles: A eukaryotic lineage including diatoms, brown algae, and organisms with distinctive hairy flagella. Stramenopiles are another proposed component of the chromalveolate grouping.
Hacrobia: A proposed eukaryotic grouping that combines haptophytes and cryptophytes. Hacrobia treats two chromalveolate components as a separate lineage rather than part of one supergroup.
Nucleomorph: A reduced remnant of an engulfed eukaryote's nucleus retained inside a host cell. Cryptophyte nucleomorphs preserve evidence of the complex endosymbiosis underlying plastid evolution.
Plastid: A membrane-bound organelle in eukaryotic cells, including chloroplasts and related structures. The shared ancestry of plastids, rather than cell form alone, motivated the supergroup.
Haptophytes: A lineage of mostly marine photosynthetic eukaryotes, many bearing scales and a specialized haptonema. Haptophytes were included because their plastids were interpreted as sharing red-algal ancestry.

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