Spirirestis rafaelensis gen. et sp nov (Cyanophyceae), a new cyanobacterial genus from arid soils

A new cyanobacterial genus and species, Spirirestis rafaelensis, is described from soils of a semi-arid Utah jumper community in the San Rafael Swell, Utah, U.S.A. Multiple isolates of the organism have only been recovered from well-crusted, protected, and totally undisturbed soils at this site; it has not been recovered from any of the other 40 sites we have examined in the Sonoran, Mojave, Chihuahuan, Colorado Plateau, or Great Basin deserts during the last eight years. Spirirestis shares morphological characters with members of both the Scytonemataceac and Microchaetaceae, principally heterocyte formation, false branching, and presence of sheath. However, unlike the trichomes of all previously described genera in these families, most trichomes of Spirirestis are tightly spiraled. 16S rRNA sequence data suggest that Spirirestis is more closely related to members of the Microchaetaceae than to members of the Scytoncmataceae or Rivulariaceae. The data also support the maintenance of Microchaetaceae and Scytonemataceae as separate families.