Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Basidiomata: waxy-gelatinous, very pale to sometimes dark brown, convex, subspherical or more often elongate, often irregular in form, 0.3-2.5 x 0.2-0.7 mm; fertile hyphae: thick-walled, 2.5-4 µm diam., at least some with clamp connections haustorial branches: present, with clamp connections; mother cell: subspherical or ellipsoid, 3.5-4 µm in diam.; haustorial filament: 0.5 µm thick, 1-3 µm long hymenium: hyaline, containing numerous probasidia; probasidial initials: ellipsoid, proliferations occurring through the basal clamp; hyphidia and cystidia: absent basidia: when mature, 2-4-celled (in some specimens all 2-celled, in others all 4-celled), with longitudinal or oblique septa, subspherical to elongate, often distinctly stalked, 8-20(-24) x 8.5-12 µm; epibasidia: subcylindrical, 2-4 µm thick, at least 30 µm long basidiospores: sub-spherical to shortly ellipsoid, with a distinct lateral apiculus, 5-8 x 4-6 µm Anamorph: unknown. Hosts: on thalli of Usnea spp., esp. U. hirta in moist mid to high elevation forests World distribution: southwestern North America and possibly northern Europe Sonoran distribution: common in Arizona. Notes: This is the fifth species of heterobasidiomycetes known to grow on Usnea. Cystobasidium usneicola Diederich & Alstrup is easily distinguished by the very distinct basidia consisting of two parts: a lower, thick-walled probasidium and an upper, thin-walled, cylindrical meiosporangium. Also its basidiospores have a terminal, refractive apiculus. Biatoropsis usnearum Räsänen is distinguished by its elongate-claviform basidia with transverse septa. Tremella santessonii Diederich also has elongate basidia, each with one transverse septum. Tremella stevensiana Diederich was the only known species on Usnea with longitudinal basidial septa. The latter Tremella species is distinguished from T. nashii by its constantly 2-celled basidia, its much smaller, applanate to pulvinate basidiomata, 0.1-0.3(-0.5) mm diam., and especially by the presence of abundant conidiophores, located between the basidia, consisting of a 9-21 µm long conidiogenous cell, bearing in the upper part 5-30 ellipsoid conidia.