Twin Map Lichen

Appearance

Thallus: crustose, areolate, verrucose

Prothallus: black among the areoles

Areoles: rounded, flat to more often convex, 0.3-0.8 mm in diameter.

Surface: usually gray, sometimes gray-brown, somewhat pruinose

Cortex: thin, 5-15 µm thick, overlain with an epinecral layer 5-15 µm thick

Apothecia: black, adnate, 0.4-0.6(-1) mm in diameter.

Disc: black, flat or becoming convex, dull

Margin: at first thick, then mostly absent

Naming

Synonyms: Rhizocarpon concretum, Rhizocarpon disporum

Distribution

Throughout western and northern North America and Greenland, Europe, and South America.

Habitat

Typically, in cold and wet regions.