Gymnoderma


Gymnoderma is a genus of lichen-forming fungi in the family Cladoniaceae. Originally established in 1860 by the Finnish lichenologist William Nylander, this small genus is characterised by forming mats of small, yellow-green scales dotted with spherical brown fruiting bodies. The genus is distinguished from related lichens by a unique microscopic feature: its spore-containing structures turn deep blue when stained with iodine, which is uncommon among members of the Cladoniaceae.

Taxonomy

The genus was circumscribed by the Finnish lichenologist William Nylander in 1860. Nylander assigned Gymnoderma coccocarpum as the type species in 1869; this species was originally collected from the Himalayas. Historical confusion affected allied names: Edvard Vainio's genus Baeoderma has been overlooked in some sources but is referable to Gymnoderma. Re-examination of Mascarenes material from Mauritius and Réunion shows that Nylander's African taxon is the same species as G. coccocarpum, extending Gymnoderma to Africa; this synonymy rests on morphology, as matching DNA sequences were not available for those island specimens. Earlier misplacements, for example confusion with Bunodophoron madagascareum, have been clarified.
Multi-locus phylogenies of Cladoniaceae place Gymnoderma in a clade close to Carassea and Pycnothelia, sister to the much larger genus Cladonia. Within the Cladoniaceae, the key diagnostic for Gymnoderma is its entirely amyloid ascus, a feature repeatedly reported and used to delimit the genus.

Description

The thallus forms overlapping with a green-yellow upper surface and a white lower surface; the margins are . Podetia are absent or very short in Gymnoderma, and when present they are solid and arise at the squamule margins. Fruiting bodies are common; they are pale brown, more or less spherical, and . In practical terms, a mat of yellow-green scales dotted with small brown balls is a typical field appearance for the genus.
Microscopically, the ascus is entirely amyloid which is an uncommon state in Cladoniaceae and helps separate Gymnoderma from superficially similar genera.

Species

Some species once classified in Gymnoderma have since been transferred to other genera. These include: