Thallus: orbicular, small, rarely bigger than 1.5 cm diam., sometimes confluent with other thalli lobes: short (3 mm) and mostly less than 0.5 mm wide, eciliate upper surface: whitish gray to dark gray with darker lobe tips, sometimes pruinose, with short, white to black hairs; soredia and isidia absent upper cortex: paraplectenchymatous medulla: white lower cortex: prosoplectenchymatous lower surface: white to brownish gray, with concolorous or darker rhizines Apothecia: usually abundant and short stalked, very variable in size, up to 2 mm diam., with thick margins; disc: dark brown to black, without pruina. ascospores: brown, 1-septate, Physcia-type, (14-) 15-18 (-21.5) x (6.5-) 7.5-9.5 (-11) µm Pycnidia: usually abundant, immersed, appearing as black warts conidia: subcylindrical, 4-6 x 1 µm Spot tests: cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C-, KC-, P- Secondary metabolite: upper cortex with atranorin. Substrate and ecology: growing on Idria columnaris and desert shrubs World and Sonoran distribution: so far known only from Baja California where it occurs with the endemic tree Idria columnaris and also from two islands off the coast. Notes: Physcia villosula is recognized by the small size, the abundant apothecia and the hairs on the upper surface. These hairs may sometimes be very sparse. The species is similar to P. stellaris, but it is much smaller and has hairs on the upper surface. Small specimens of Heterodermia erinacea might be similar to P. villosula but can easily be separated by the prosoplectenchymatous upper cortex. If soredia are missing on P. adscendens it might be difficult to separate it from P. villosula. Because even small specimens of the latter have apothecia and hairs on the upper surface, it is usually no problem to separate them.