Porpidia macrocarpa

Appearance

Thallus: crustose, very variable, from partially immersed to continuous, rimose or areolate, up to 12 cm in diam, up to 0.4 mm thick, sometimes with an indistinct gray to black prothallus areoles: irregularly shaped, 0.4-0.5(-0.8) mm in diam. surface: white, pale gray, greenish gray or olive, red, rarely orange, rough, rugose cortex: hyaline or occasionally encrusted with orange crystals above, 20-30 µm thick, lacking an epinecral layer medulla: white, I-, with hyphae 3.5-4 µm in diam.; algal layer: 60-65 µm thick with cells 9-10(-14) in diam Apothecia: +round, sessile, constricted at base, 0.1-2(-4) mm in diam. disc: black or brownish black, subconcave to plane or convex, dull, epruinose to weakly grayish or whitish pruinose margin: usually distinct, rarely becoming indistinct, black or occasionally rusty red, entire to rarely flexuose or crenulate

Distribution

World distribution: throughout temperate and arctic or alpine areas in Europe, Asia, North America, and Australasia

Habitat

Substrate and ecology: on siliceous rocks and boulders, less often on pebbles and very rarely on wood