Porpidia crustulata

A saxicolous lichen on siliceous rocks, with a pale grey to whitish thallus and minute disc-shaped black apothecia 0.5 to 1.5 mm across, irregularly arranged although sometimes forming concentric circles, with a clearly defined prothallus/growth margin.

Asci clavate, eight-spored, 60 to 80 µm long, 12 to 20 µm wide, with biseriate to irregular spore arrangement inside the ascus, and an amyloid apical reaction in Melzer's reagent.

Paraphyses filiform, septate, profusely branched and anastomosed, 1.5 to 1.8 µm wide at the base, with slight apical enlargements of 2 to 3.5 µm, apically covered by a blackish-brown amorphous encrusting extracellular substance, and exceeding the height of the asci.

Ascospores ellipsoidal, smooth, hyaline, thin-walled, 12.5 to 15 µm long, 6 to 8 µm wide, with dense cytoplasm of slightly granular appearance consisting of small refractive spherical lipid bodies.