The heterokonts or stramenopiles are a major line of eukaryotes presently containing about 10,500 known species. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which are a primary component of plankton. Other notable members of the Stramenopila include the (generally parasitic) oomycetes, including Phytophthora of Irish potato famine infamy and Pythium which causes seed rot and damping off.
Most basal heterokonts are colorless, suggesting they diverged before aqcuisition of chloroplasts within the group. However, fucoxanthin-containing chloroplasts are also found among the haptophytes, and evidence suggests that the two groups have a common ancestry, as well as possible a common phylogenetic history with cryptomonads. In this case the ancestral heterokont was an alga, and all colorless groups arose through loss of the secondary endosymbiont and hence its chloroplast.
Mastigonemes are manufactured from glycoproteins in the cell's endoplasmic reticulum before being transported to its surface. When the tinsel flagellum moves, these create a backwards current, pulling the cell through the water or bringing in food. The mastigonemes have a peculiar tripartite structure, which may be taken as the defining characteristic of the group, thereby including a few protists that do not produce cells with the typical heterokont form. They have been lost in a few lines, most notably the diatoms.
In this scheme, however, the Chrysophyceae are paraphyletic to both other groups. As a result, various members 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 - for instance 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 them among the heterokonts. Should it turn out that they evolved from colored ancestors, the 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 ranks. 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 Chromalveolata, together with the haptophytes, cryptomonads and alveolates. This is one of the most common revisions to the five-kingdom system, but has not been generally adopted, partly because some biologists doubt their monophyly. A few treat the Chromalveolata as identical in composition with the heterokonts, or list them as a kingdom Stramenopila.
The origin of the name stramenopile is explained by Adl and coauthors:
Regarding the spelling of stramenopile, it was originally spelled stramenopile. The Latin word for ‘‘straw’’ is stramine-us, -a, -um, adj. [stramen], made of straw—thus, it should have been spelled straminopile. However, Patterson (1989) clearly stated that this is a common name (hence, lower case, not capitalized) and as a common name, it can be spelled as Patterson chooses. If he had stipulated that the name was a formal name, governed by rules of nomenclature, then his spelling would have been an orthogonal mutation and one would simply correct the spelling in subsequent publications (e.g. Straminopiles). But, it was not Patterson’s desire to use the term in a formal sense. Thus, if we use it in a formal sense, it must be formally described (and in addition, in Latin, if it is to be used botanically). However, and here is the strange part of this, many people liked the name, but wanted it to be used formally. So they capitalized the ﬁrst letter, and made it Stramenopiles; others corrected the Latin spelling to Straminopiles.