Lecidea lithophila

General: Crustose saxicolous lichen restricted to acidic siliceous rocks with high iron content, thallus greyish-white mottled with conspicuous rust-red patches resulting from iron oxide uptake from the substrate.

Apothecia: Abundant, flat, compact, black, turning reddish-brown when wet, 0.5-2 mm in diameter. Thallus K- (no reaction).

Asci: Clavate, 8-spored, thick-walled, 43-50 x 7-12 µm, spores biseriate to irregular, strongly amyloid in Melzer's reagent.

Paraphyses: Slender, 1.5-2 µm thick, mostly simple with occasional apical branches, septate, terminal cell enlarged (clavate to subcapitate, 3-4.5 µm wide) and capped with an amorphous dark brown pigment cap.

Ascospores: Ellipsoid, smooth, hyaline, thin- to slightly thick-walled, 9-13 x 4.5-5.5 µm, containing two large polar oil guttules, unicellular and aseptate.