Athelia Pers.
Type : * Athelia epiphylla Pers.
Description : Basidiomata consisting of a thin, white, whitish or cream, arachnoid skin easily separated from substratum. Hyphae hyaline, with or without clamps, often encrusted with crystals, those of the subhymenial layer often broader and with thicker walls. Cystidia absent. Basidia often clustered, clavate, tapering gradually towards base, mostly short, with 2–4-sterigmata. Basidiospores of various shapes, Hyaline, thin-walled I−.
The widespread basidomycete (Stereales) genus Athelia is accommodated in the family Atheliaceae (Kirk et al. 2001). Some 28 species are recognised (Jülich 1972, 1978; Diederich 2004c). One species, Athelia arachnoidea, which is present in New Zealand, is an important pathogen of lichens (especially of Lecanora conizaeoides in the Northern Hemisphere) and of epiphytic green algae and mosses on trees in urban, especially inner city habitats. This fungus is common in urban and industrialised areas of the Northern Hemisphere, where it is easily recognised by its seasonal, parasitic nature, growing on epiphytes on standing trunks in parks and gardens. A. arachnoidea attacks free-living algae (e.g. Desmococcus) as well as photobionts of lichens, forming lesions of white circles up to 15 cm diam., similar to mould colonies. The lesions often coalesce to produce extensive areas of damage. An attack results in the rapid death of algae and lichens, and appears to be favoured by moderate to heavy levels of air pollution (Arvidsson 1976, 1979; Christiansen 1980; Gilbert 1988; Diederich 1989; Parmasto 1998; Yurchenko & Golubkov 2003). In the Northern Hemisphere A. arachnoidea is evidently active only during the winter months probably as a result of higher humidity (Gilbert 1988; Parmasto 1998).
