Anamorph: Thallus white, arachnoid. Consisting of active mycelia surrounding a dying central zone. Four types of vegetative hyphae known. 1. Simple, rarely branching hyphae 4-5 µm wide, smooth or lightly encrusted with calcium oxalate crystals, with both simple and clamped septa. This hyphal type occurs mainly in the marginal zone of the thallus actively colonising algal cells and lichen thalli. Sometimes joined to form fascicles 10-14 µm wide. 2. More or less straight hyphae with few branches, 3.3-6 µm wide, variably encrusted, with simple or clamped septa, occurring mainly in the centre of the thallus. 3. Straight hyphae ± richly branched with branches at right-angles, anastomosing, 2.7-3.3 µm wide, with some encrusting crystals and with scattered clamps. 4. Sinuous, richly branched hyphae, (1.7-)3-3.3(-5.5) µm wide, with occasional clamps and some encrusting crystals. Occurring in contact with living and dying algal cells in central parts of the thallus. Sclerotia pale, beige to brown, globose or sometimes flattened, 0.1-0.2 mm in diameter when dry, scattered in groups on mycelium. Central cells in sclerotia short and broad, 6-15.5 x 5-15 µm, with thickened walls.
Teleomorph: Basidiomata rarely seen. Composed of a white or cream, discontinuous and fissured hymenium, often sterile with basidioles only. Subicular hyphae 3.3-5 µm wide, with thickened walls, branched, with scattered crystalline incrustations and some clamps. Subbasidial hyphae 2.5-3.3(-6) µm wide, with thin or slightly thickened walls, hyaline with some minute guttules and clampless septa, smooth to richly encrusted (crystals partially dissolving in KOH). Basidioles clavate, smooth or with few crystals, with clampless thin septa. Basidia short clavate or subcylindrical, 21-24 x 5-6.3 µm, usually with two straight or curved sterigmata 5-11(-13.5) x 1-1.7 µm. Spores hyaline, ellipsoid, 6-7.5 x 2.7-3.7 µm.
Description adapted from Yurchenko & Golubkov (2003).
Causes large areas of damage on algae and lichens on tree bark, especially in urban areas in the UK. Damaged areas have a white edge where hyphal growth is thickest. Infections are usually visible from a distance. No other fungus causes such large areas of damage except for Chromocyphella muscicola which destroys mosses on bark resulting in a yellow margin to the damaged areas due to dying moss. No hyphae are visible to the naked eye. Fruiting bodies of this fungus are small white caps. Athelia epiphylla grows on bark and is also often sterile.
In the UK, most commonly found in urban areas on tree trunks in communities dominated by Physcia adscendens and Xanthoria parietina. Can also infect other lichens in other habitats but always over bark.
Mainly recorded from the south and east of the UK.