Overview
Heterokonts (also known as stramenopiles) form a large and varied branch of eukaryotic life that includes more than 100,000 described species, most notably the diatoms. These organisms range from microscopic, single-celled plankton to large multicellular seaweeds. Modern summaries of their diversity and relationships can be found in many survey works and databases (classification overview).

Defining characteristics

Heterokonts are best known for a life stage in which cells bear two unequal flagella: one smooth and one with rows of tripartite hairs (the "tinsel" flagellum). This pair is the feature that inspired both the name heterokont (different flagella) and stramenopile (straw-like hairs). Many heterokonts that perform photosynthesis possess plastids derived from a red algal ancestor, with accessory pigments such as fucoxanthin that give brown and golden tones. Structural adaptations vary widely: diatoms build silica shells, brown algae form complex tissues, and some groups lack plastids entirely.

Major groups and examples

  • Diatoms – unicellular or colonial algae with silica frustules; major marine and freshwater primary producers (diatoms).
  • Brown algae (Phaeophyceae) – multicellular seaweeds including kelp and Sargassum that form habitats in coastal zones (brown algae, kelp, Sargassum).
  • Oomycetes – water molds and related organisms, some of which are pathogens of plants and animals.

History and classification

Heterokonts were long grouped within broader assemblages such as Chromalveolata (kingdom Chromalveolata), but molecular phylogenies have prompted revisions. Many modern treatments place them in the SAR supergroup alongside alveolates and rhizarians; different authors use the names "heterokont" and "stramenopile" to emphasize morphology or phylogeny. For accessible summaries of their evolutionary placement see curated resources (algal overview, life cycle notes).

Ecological and economic importance

Heterokonts are ecologically pivotal. Diatoms drive large portions of marine photosynthesis and the biological pump that sequesters carbon to the deep ocean. Brown algae form kelp forests that support fisheries and coastal biodiversity. Some oomycetes have major agricultural impacts as plant pathogens. Humans use heterokont products such as alginates from brown algae, diatomaceous earth in filtration and abrasives, and diatoms as indicators in environmental monitoring (seaweeds and uses).

Notable distinctions and facts

Although commonly called "algae," heterokonts include non-photosynthetic lineages and organisms with complex life cycles. Their plastids generally reflect a secondary endosymbiotic origin and carry pigments different from green algae. Diagnostic features such as the tinsel flagellum, silica frustules in diatoms, and the large size range among brown algae help differentiate heterokonts from other algal groups. For further reading and data portals consult specialist sites and taxonomic databases (Sargassum notes, classification overview, historical context, life cycle notes, diatom resources, algal overview, brown algae, commercial uses, kelp biology).