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Rhizocarpon disporum (Naeg. ex Hepp) Mull. Arg.
Family: Rhizocarpaceae
[Buellia montagnei (Flot.) Tuck.,  more]
Rhizocarpon disporum image
Stephen Sharnoff  
Life habit: lichenized, not lichenicolous Thallus: crustose, areolate; prothallus: distinct areoles: flat to warty convex or almost globose, without differentiated margins, 0.2-1 mm in diam. surface: gray to gray-brown, rarely distinctly brown (mostly due to abrasion or injury), dull cortex: brown above, 5-15 µm thick, overlain with c. 10 µm thick epinecral layer Apothecia: black, 0.4-0.9 mm wide disc: black, convex margin: black, thin or mostly absent exciple: colorless with black margin epihymenium: red-brown to brown-black, partly fused into a pseudoparenchymatous tissue, K+ red hymenium: hyaline, 100-150 µm tall; paraphyses: tips fused into a pseudoparenchymatous tissue; hypothecium: brown asci: clavate, 1-spored ascospores: brown to dark brown, muriform, ellipsoid, 4878 x 18-33 µm Pycnidia: frequent, black, globose, on the prothallus conidia: hyaline, filiform, 8-14 x 0.3-0.6 µm Spot tests: thallus usually K+ weakly yellow or rarely K+ strong yellow or K-, P- or P+ reddish Secondary metabolites: +norstictic acid. Substrate and ecology: on siliceous rocks, including sandstones World distribution: in semi-arid regions of western North America, Greenland, Europe and South America (Bolivia) Sonoran distribution: Arizona, southern California, Baja California, Sonora and Chihuahua.