Kelp, diatoms and potato blight share one odd hairy family trait
A giant kelp, a glassy diatom and the mould behind the potato blight look nothing alike, yet they belong to one lineage, the stramenopiles. What ties them together is a peculiar three-part hair on their flagella, shaped like a straw tipped with fine bristles. Even diatoms that lost those hairs still carry the genes for them.
Stramenopiles, also called heterokonts, are a huge branch of eukaryotes. Most are single cells, but the brown algae, including wracks and kelps, grow large and many-celled. Most produce swimming cells at some point, typically with two unequal flagella: the front one carries rows of stiff hairs, while the rear one is smooth and usually shorter. Each hair has a flexible base, a long rigid tube, and a tuft of delicate mastigonemes at the tip. The name stramenopile, coined by D. J. Patterson in 1989, borrows the Latin for straw, the stramen of that tube.
The older word heterokont caused a century of confusion. Alexander Luther introduced Heterokontae in 1899 for algae now called Xanthophyceae, and later authors stretched it over unrelated groups, including Herbert Copeland in 1956. Patterson's term cleared this up, and the International Society of Protistologists made Stramenopiles formal in 2005. Along with Alveolata and Rhizaria, they form the SAR supergroup, named from their initials.
Many photosynthesise with plastids tinted golden, orange or brown by chlorophyll c and fucoxanthin. These plastids are wrapped in four membranes, a trace of an ancient red alga captured by the SAR ancestor. Molecular evidence suggests the earliest stramenopiles were colourless and ate other organisms, gaining plastids only later. Diatoms are now among the most important primary producers in seas and fresh water and major players in global carbon cycling.
Other members live very differently. Phytophthora infestans, an oomycete, causes potato blight, and Blastocystis lives as a gut parasite in humans. Opalines inhabit the intestines of cold-blooded vertebrates. A tiny bacteria-eater named Cafeteria is common worldwide, recycling nutrients through microbial food webs. A flagellate found in 2023, Kaonashia insperata, still has no settled place on the family tree.
Source: Stramenopile
