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Rhizocarpon arctogenum Gelting
Family: Rhizocarpaceae
Rhizocarpon arctogenum image
Life habit: lichenized, not lichenicolous Thallus: crustose, 04-0.8 mm wide; prothallus: black, with diffuse to radiate edges areoles: peltate, round or angular, convex, 0.4-0.8 mm wide surface: brown to blackish brown, often shiny, with gray pruinose margins; underside dark Apothecia: grouped or dispersed, adnate or sessile among areolae disc: black, becoming roughened and convex, epruinose margin: thin, persistent or disappearing exciple: dark brown in exterior, paler within epihymenium: brown or slightly violet, K- or K+ more violet hymenium: hyaline or pale violet, 120-150 µm tall; paraphyses: brown, upper cells partly constricted, c. 2 µm wide below, 3-4 µm wide apically; hypothecium: brown to black, K- asci: clavate, 4-5-spored ascospores: olive-brown to dark brown, muriform, oblong-ellipsoid, often slightly bent, becoming dark, 30-46 x 14-20 µm Pycnidia: not seen Spot tests: medulla K-, C+ red (areolae on same thallus), KC+ red, P-; I+ blue Secondary metabolites: probably gyrophoric acid when C+ red. Substrate and ecology: on siliceous rocks in dry to slightly moist areas and on rocks in snowmelt areas World distribution: Greenland and Arizona Sonoran distribution: Arizona.