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Rhizocarpon pusillum Runem.
Family: Rhizocarpaceae
Rhizocarpon pusillum image
Life habit: lichenicolous Thallus: crustose, areolate, forming patches within the host's thallus, up to 1 cm in diam., without a prothallus areoles: developing from the host's areoles, round to angular, weakly to strongly convex, up to 0.6 mm in diam. surface: bright yellow, smooth, epruinose medulla: white, KI- Apothecia: round or angular, up to 0.7 mm in diam. disc: black, weakly convex or strongly convex, epruinose exciple: reddish brown epihymenium: brown, K+ red, not containing crystals hymenium: hyaline, 60-90 µm tall; paraphyses: capitate; hypothecium: brown asci: clavate, 8-spored ascospores: hyaline or pale green-brown initially, becoming dark green to brown, 1-septate, 9-15 x (4-)6-7 µm, halonate Spot tests: medulla K-, C-, P+ yellow Secondary metabolites: rhizocarpic and psoromic acids. Substrate and ecology: on non-calciferous rock in the alpine zone at 3600 m (single locality) Host: Sporastatia testudinea World distribution: Asia, Europe, North America and New Zealand Sonoran distribution: Arizona (San Francisco Peaks).