SAR (clade)

SAR is a highly diverse clade of eukaryotes, often considered a supergroup, that includes stramenopiles (heterokonts), alveolates, and rhizarians. It is a node-based taxon (under the Sar name), including all descendants of the three groups' last common ancestor, and comprises most of the now-rejected Chromalveolata. Their sister group might be telonemids, with which they would make up the TSAR clade, but this grouping has been challenged.

Etymology

The name SAR is an acronym derived from the first letters of its three constituent clades (Stramenophiles, Alveolata, Rhizaria); it has been alternatively spelled RAS. The term Harosa (at the subkingdom level) has also been used, with Stramenopiles replaced by its synonym Heterokonta in this variant of the acronym.

History of discovery

Before the discovery of the SAR supergroup, stramenopiles and alveolates were classified in the supergroup Chromalveolata alongside haptophytes and cryptomonads, being believed to have acquired plastids through secondary endosymbiosis of red algae through a common ancestor. Meanwhile, Rhizaria was traditionally considered to be a separate supergroup. More recent phylogenetic studies confirmed that stramenopiles and alveolates diverged with rhizarians as part of the SAR lineage. This clade has been found by later phylogenomic studies to be robustly characterized compared to other supergroups.

This group excludes haptophytes and cryptomonads, hypothesized to have acquired plastids in separate endosymbiosis events, leading Okamoto et al. (2009) to propose the clade Hacrobia to accommodate them.