Heterokont

In 1899, Alexander Luther created the term "Heterokontae" for some algae with unequal flagella, today called Xanthophyceae.[11] Later, some authors (e.g., Copeland, 1956) included other groups in Heterokonta, expanding the name's sense. The term continues to be applied in different ways, leading to Heterokontophyta being applied also to the phylum Ochrophyta. The term 'Stramenopile' was introduced in 1989 by Patterson [12] to overcome ambiguities that had (and continue to be) developed with the use of the term 'heterokont'. Consequently, heterokonts may be referred to as stramenopiles.

The term 'heterokont' first emerged in the context of 19th century phycology. Over time, the scope of application has changed; especially when in the 1970's as ultrastructural studies revealed greater diversity among the algae with chromoplasts (= chlorophylls a and c) than had previously been recognized. At the same time, a protistological perspective was replacing the 19th century one based on the division of unicellular eukaryotes along inappropriate botanical/zoological lines. One consequence was that an array of heterotrophic organisms, many of which had not been previously considered as 'heterokonts' were seen as being related to the 'core heterokonts' (i.e. those having anterior flagella with stiff hairs). Newly recognized relatives included the parasitic opalines, proteromonads, and actinophryid heliozoa. They joined other heterotrophic protists, such as bicosoecids, labyrinthulids, and oomycete fungi, that were included by some as heterokonts and excluded by others. Rather than continue to use a name whose meaning had changed over time and was hence ambiguous, the name 'stramenopile' was introduced to refer to the clade of protists that had tripartite stiff (usually flagellar) hairs and all their descendents. Molecular studies confirm that the genes that code for the proteins of these hairs are exclusive to stramenopiles.[13] As the concept of 'Stramenopile' is based on a presumed apomorphy, it is stable and robust even when its composition changes. There is a widespread presumption, as here, that the terms 'stramenopile' and 'heterokont' are synonyms. They are not because they are defined differently and despite compositional overlap, most applications of the names imply differing compositions.

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 the haptophytes, cryptomonads, and alveolates. This is one of the most common revisions to the five-kingdom system, but has not been adopted, because Chromalveolata is not a monophyletic group. A few treat the Chromalveolata as identical in composition with the heterokonts, or list them as a kingdom Stramenopila.

Some sources divide the heterokonts into the autotrophic Ochrophyta and heterotrophic Bigyra and Pseudofungi.[15] However, some modifications to these classifications have been suggested.

The name Heterokonta can be confused with the (much older) name Heterokontae, which is generally equivalent to the Xanthophyceae, a limited subset of the Heterokonta.[16]

The simplified classification of the group according to Adl et al. (2012), in which heterokonts (using the term Stramenopiles) are part of a larger clade that embraces Alveolates and Rhizaria, is:[17]

Eukaryota

• SAR
  • Stramenopiles Patterson, 1989, emend. Adl et al., 2005
    • Opalinata Wenyon, 1926, emend. Cavalier-Smith, 1997 (Slopalinida Patterson, 1985)
    • Blastocystis Alexeev, 1911
    • Bicosoecida Grassé, 1926, emend. Karpov, 1998
    • Placidida Moriya et al., 2002
    • Labyrinthulomycetes Dick, 2001
    • Hyphochytriales Sparrow, 1960
    • Peronosporomycetes Dick, 2001 (Öomycetes Winter, 1897, emend. Dick, 1976)
    • Actinophryidae Claus 1874, emend. Hartmann 1926
    • Bolidomonas Guillou & Chrétiennot-Dinet, 1999 (Bolidophyceae in Guillou et al., 1999)
    • Chrysophyceae Pascher, 1914
    • Dictyochophyceae Silva, 1980
    • Eustigmatales Hibberd, 1981
    • Olisthodiscophyceae Barcytė, Eikrem & M.Eliáš, 2021[18][19]
    • Pelagophyceae Andersen & Saunders, 1993
    • Phaeothamniophyceae Andersen & Bailey, in Bailey et al., 1998
    • Pinguiochrysidales Kawachi et al., 2003
    • Raphidophyceae Chadefaud, 1950, emend. Silva, 1980
    • Synurales Andersen, 1987
    • Xanthophyceae Allorge, 1930, emend. Fritsch, 1935 (Heterokontae Luther, 1899, Heteromonadea Leedale, 1983, Xanthophyta Hibberd, 1990)
    • Phaeophyceae Hansgirg, 1886 (not Kjellman, 1891, not Pfitzer, 1894)
    • Schizocladia Henry et al., in Kawai et al., 2003 (Schizocladales Kawai et al., 2003) (M)
    • Diatomea Dumortier, 1821 (= Bacillariophyta Haeckel, 1878)
  • Alveolata
  • Rhizaria

Based on the following works of Ruggiero et al. 2015 & Silar 2016.[20][21][22]

• 
  Aplanochytrium (Labyrinthulea)
• 
  Blastocystis hominis (Blastocystea)
• 
  Protoopalina pingi (Opalinea)
• 
  Peronospora sparsa (Oomycetes)
• 
  Potatoes with Phytophthora (Oomycetes)
• 
  Diatoms (Bacillariophyceae)
• 
  Silicoflagellate (Dictyochophyceae)
• 
  Actinophrys sol (Actinophryida)
• 
  Nannochloropsis sp. (Eustigmatophyceae)
• 
  Dinobryon sp. (Chrysophyceae)
• 
  Synura sp. (Synurophyceae)
• 
  Gonyostomum semen (Raphidophyceae)
• 
  Vaucheria (Xanthophyta)
• 
  Fucus distichus (Phaeophyceae)
• 
  Pelagophycus porra (Phaeophyceae)

Wikispecies has information related to Heterokonta.

• Tree of Life Web Project: Stramenopiles