ABSTRACT: Description is provided of Caloplaca nashii sp. nov., a saxicolous-calcicolous lichen growing on caliche in arid regions of Baja California (Mexico). It is related to the C. lactea group by its poorly developed thallus, lacking anthraquinones, and spores with short wall thickening (isthmus) less than 3 µm. however, it differs from the known species of this group by having shorter and narrower ellipsoid spores, (10)11.5-16(19.5) x (4)4.5-6 µm. Caloplace lactea var. americana is considered as a probable synonym of C. holocarpa.

KEYWORDS: Caloplaca, taxonomy, new species, Baja California, Mexico

NOMENCLATURAL NOVELTIES:
Caloplaca nashii Nav.-Ros., Gaya & Hladun, p. 31