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KINGDOM HETEROKONTAE

The Kingdom Heterokontae includes those taxa with tubulocristate mitochondria that produce the heterokont motile cell, a heterodynamic cell with paired flagella: one an anteriorly-directed tinsel flagellum and the other a recurrent or posteriorly-directed whiplash flagellum.  There are variations on that theme; however, when there are pairs of basal bodies, they are anchored by four flagellar roots (Patterson 1999).   Some of these taxa are variously called Stamenopiles (Patterson 1989) or Chromista (Cavalier-Smith 1989).  They are in a coherent clade of crown eukaryotes of ten phyla in this system. They are recognized as a natural group joined by tripartite tubular hairs on their flagella as a major synapomorphy, although some taxa have secondarily lost this character (Patterson 1989 and 1999; Andersen 1991; Leipe et al. 1994; Saunders et al. 1994; Silberman et al. 1996; and Cavalier-Smith 1989).    I included Opalinota because of ribosomal RNA similarities. Indeed, I have used the phylogeny of Sogin and Patterson (Tree of Life Project) to address the questions of the opalinids and other relationships in the kingdom. The kingdom varies from multiflagellated unicells to large (many meters long) multicellular kelps, a diversity in form that rivals that of the Plant Kingdom.  

Cavalier-Smith (1986) united most of the photosynthetic heterokonts into a single phylum, the Ochrophyta, a taxon adopted by Graham and Wilcox (2000) to include the diatoms, raphidiophytes, chrysophytes, eustigs, silicoflagellates, xanthophytes, and phaeophytes.  Although these taxa do seem to be part of the same clade, I interpret them as related within the same subkingdom because of the enormous variation between these groups.

Until recently the heterokonts were among the groups included in the "crown eukaryotes"; however, work summarized by Baldauf (2003) presents a very different picture of eukaryote evolution.  New phylogenies based on many molecular and ultrastructural relationships indicate that the eukaryotes occupy eight great "clades" called supergroups, one of which is the heterokonts.  In her synthesis, though, Baldauf (2003) has the cryptomonads and haptomonads associated with the base of the typical heterokont - alveolate line in a sister group relationship.  Harper et al. (2005) use a 6-protein phylogeny of eukaryote taxa and provide strong evidence that the Heterokonts are part of a larger clade (alveolates+heterokonts) and have a weak association with the cryptomonad+haptomonad clade.  Keeling (2004) also suggests the same relationship in a supergroup called the chromalveolates [formalized to Chromalveolata]. (The Domain Eukarya Page).

A more complete taxonomy (to the ordinal level) of the Kingdom Heterokontae.

Concepts and Terms.

REFERENCES.

This page written and maintained by Jack R. Holt.  Last modified: 04/22/08