Arthrospira

Arthrospira and Limnospira are two genera of free-floating filamentous cyanobacteria characterized by cylindrical, multicellular trichomes in an open left-hand helix. A dietary supplement is made from L. platensis and L. maxima, known as spirulina.

The two species species were commonly treated as if they are in the genus Spirulina since 1932, even though they were originally proposed in Arthorospira in 1892 and 1917. The distinction was restored in the late 20th century. Although the introduction of the two separate genera Arthrospira and Spirulina is now generally accepted, there has been much dispute in the past and the resulting taxonomical confusion is tremendous. To add to the problem, it was shown in 2019 that the type species for Arthrospira, A. jenneri, was very distantly related to the species used in food production. This necessitated the creation of yet another genus, Limnospira, to hold these economically-important species.