Stramenopile

Stramenopiles, also called heterokonts, are a diverse lineage of eukaryotes within the SAR supergroup. They include both photosynthetic organisms such as diatoms and brown algae and heterotrophic groups such as the water molds (oomycetes), making the group one of the most ecologically and economically important lineages of algae and fungus-like organisms.

A hallmark of many stramenopiles is the heterokont condition: during certain life stages they bear two flagella of different types—one long and smooth (whiplash) and one shorter, densely hairy (tinsel). Their plastids typically arose by secondary endosymbiosis with red algae, and cell walls are commonly cellulose-rich. Nutritional modes are diverse, including photosynthesis, absorptive heterotrophy, and mixotrophy.

Major lineages include diatoms (Bacillariophyta), which have intricate silica cell walls; brown algae (Phaeophyceae), which form large seaweeds and kelp forests; golden algae (Chrysophyceae) and yellow-green algae; and oomycetes (oomycota), the water molds that are important plant pathogens and saprotrophs. The group spans life cycles from unicellular plankton to complex multicellular thalli, with varying reproductive strategies.

Ecology and significance: stramenopiles are major contributors to photosynthetic productivity in aquatic ecosystems. Diatoms play a key role in global carbon cycling and silica deposition, while brown algae support kelp forest ecosystems. Oomycetes include several important plant pathogens. Taxonomically, stramenopiles are placed within the SAR supergroup; historically they were grouped with other protists and, in older classifications, were sometimes treated as a separate kingdom, Chromista.