Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: umbilicate, usually monophyllous to almost polyphyllous, lobate, soft, thin, often with a lacerated margin, 2-5(-12) cm in diam. upper surface: light gray to light green, smooth initially but developing a fine network of fissures, dissolving into patchy or flake-like soredia marginally medulla: white lower surface: white to pink, covered densely with long, often darker centrally, slender, slightly branched rhizionomorphs (hirsutus = hairy) Apothecia: not common, black, sessile to stipitate, gyrose, up to 2 mm in diam. asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 10-14 x 4-8 µm Spot tests: medulla K-, C+ red , KC+ red P- Secondary metabolites: gyrophoric and lecanoric acids. Substrate and ecology: on silicious rocks in boreal zone, mostly on steeply inclined surfaces which regularly have seeping water; hygrophilic World distribution: Europe, Asia, and North America Sonoran distribution: rare in southern California. Notes: Umbilicaria hirsuta is the only species of Umbilicaria in the Sonoran region that reproduce primarily by soredia.