Heterokonts

Heterokonts, also known as Stramenopiles, are a major lineage of eukaryotes within the SAR supergroup. They comprise a broad and diverse set of organisms, including diatoms, brown algae, golden and yellow-green algae, chrysophytes, and the fungus-like oomycetes (water molds). A traditional unifying feature is the structure of their motile life stages: most heterokonts possess two flagella of different morphology, typically with one smooth and the other bearing tubular hairs called mastigonemes. Although this flagellar distinction is a key diagnostic trait, several lineages have reduced or lost flagella in certain life stages.

The group encompasses both photosynthetic and heterotrophic taxa. Diatoms are notable for their ornate siliceous cell walls and are major contributors to marine and freshwater phytoplankton. Brown algae form large marine seaweeds and kelp forests. Chrysophytes and other golden or yellow-green algae inhabit a range of aquatic environments. Oomycetes include many important plant and animal pathogens, such as Phytophthora species. Life cycles and reproductive strategies vary widely across heterokonts, with some groups exhibiting alternation of generations and others having simpler haplontic or diplontic lifestyles.

In terms of classification, heterokonts are a key clade within the larger Stramenopiles and the SAR supergroup. Molecular phylogenies consistently place them together as a distinct lineage, highlighting their early divergence from other eukaryotes. The diversity of forms and ecologies within heterokonts reflects a long evolutionary history, from microscopic planktonic diatoms to large multicellular macroalgae.