chlorophyll a and chlorophyll c, and usually the accessory pigment fucoxanthin, giving them a golden-brown or brownish-green colour. Because of this colour, they are referred to as 'chromoplasts' distinguishing them from chlorophyll B containing plastids of green algae, their descendants the higher plants, and euglenids. Most basal heterokonts are colorless. This suggests that they diverged before the acquisition of chloroplasts within the group. However, fucoxanthin-containing chloroplasts are also found among the haptophytes. This led to hypotheses that all organisms with chlorophyll a/c containing chloroplasts have a common phylogenetic history with cryptomonads, and should be taxonomically grouped as the Chromista. Molecular studies do not confirm that the stramenopiles, haptophytes, and cryptomonads are sister taxa. The current consensus is that the ancestral stramenopiles / heterokonts were heterotrophic and acquired chloroplasts after their defining feature (the tripartite hairs) appeared. Classification As noted above, classification varies considerably. Originally, the heterokont algae was used only for Xanthophytes. The concept morphed to include more lineages and considered by some as part of the kingdom Plantae and later, by others, as within the Protista. An example is: Division Chrysophyta Class Chrysophyceae (golden algae) Class Bacillariophyceae (diatoms) Division Phaeophyta (brown algae) In this scheme, the Chrysophyceae is conceived of a very extensive group (Chrysophyte sensu lato) that was paraphyletic - as the diatoms and brown algae evolved from within the chrysophytes. Over time, various lineages have been given their own classes and often divisions. Recent systems often treat these as classes within a single division, called the Heterokontophyta, Chromophyta, or Ochrophyta. This is not universal, however; Round et al. treat the diatoms as a division. The discovery that oomycetes and hyphochytrids are related to these algae, rather than fungi, as previously thought, has led many authors to include these two groups among the heterokonts. Should it turn out that they evolved from colored ancestors, the heterokont group would be paraphyletic in their absence. Once again, however, usage varies. David J. Patterson named this extended group the stramenopiles, characterized by the presence of tripartite mastigonemes, mitochondria with tubular cristae, and open mitosis. He used the stramenopiles as a prototype for a classification without Linnaean rank. Their composition has been essentially stable, but their use within ranked systems varies. Thomas Cavalier-Smith treats the heterokonts as identical in composition with the stramenopiles; this is the definition followed here. He has proposed placing them in a separate kingdom, the Chromalveolata, together with