Stramenopiles

Stramenopiles, also known as heterokonts, are a broad and diverse clade of eukaryotes within the SAR supergroup. They include both photosynthetic groups, such as diatoms and brown algae, and heterotrophic lineages, notably the water molds (oomycetes). A unifying feature of many stramenopiles is their motile stage bearing two differently shaped flagella: a longer, hairy flagellum with mastigonemes and a shorter smooth flagellum. In photosynthetic stramenopiles, chloroplasts are derived from secondary endosymbiosis with red algae, and pigments such as fucoxanthin give a brown to olive color in many lineages.

Within Stramenopiles, Ochrophyta encompasses most photosynthetic taxa, including diatoms (Bacillariophyta) with ornate silica cell walls, and brown algae (Phaeophyceae), large multicellular seaweeds rich in fucoxanthin. Golden algae (Chrysophyceae) and related chrysophyte groups are predominantly unicellular or colonial and typically pigment-rich. Oomycetes (water molds) form a distinct, mostly terrestrial and aquatic group of fungus-like organisms with cellulose-based cell walls and coenocytic hyphae; they produce motile zoospores with two unequal flagella and include several important plant pathogens.

Ecologically, stramenopiles are major contributors to global photosynthesis, nutrient cycling, and aquatic food webs. The group is diverse in morphology and life cycles, ranging from unicellular diatoms to complex multicellular brown algae, and molecular data continue to refine their relationships within the SAR clade.