Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. 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 Stramenopiles include the (generally) parasitic oomycetes, including Phytophthora, which caused the Great Famine of Ireland, and Pythium, which causes seed rot and damping off. The name "heterokont" refers to the type of motile life cycle stage, in which the flagellated cells possess two differently arranged flagella (see zoospore). History In 1899, Alexander Luther created the term "Heterokontae" for some algae with unequal flagella, today called Xanthophyceae. 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 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. As the concept of 'Stramenopile' is based on a presumed apomorphy, it is stable and robust even when its composition changes.