Athelia arachnoidea  

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).