Thallus: foliose, very variable, irregular, rarely orbicular, up to 5 cm diam. (often forming colonies up to 15 cm or more in diam.), loosely adnate, dichotomously lobate lobes: sublinear, elongate, radiating, the lobe-tips ascending, usually widening towards apices, c. 2-3 (-4) mm at the tips, usually discrete, sometimes dissected with lobules along the margin developing small soralia upper surface: greenish white, whitish to cream-colored, rarely brownish, sometimes pruinose at tips especially when young, sorediate soredia: farinose to granular, in labriform to capitate soralia, on lateral or terminal lobes, sometimes spreading along lobe margin upper cortex: prosoplectenchymatous medulla: white lower cortex: absent lower surface: white to brownish or bluish black, arachnoid, often sparsely spotted with a brownish orange-red pigment towards lobe apices, rhizinate; rhizines: marginal, simple, black, 1-3 (-7) mm long Apothecia: extremely rare, laminal, substipitate, 1-8 mm in diam.; margin: lacinulate; disc: concave, dark brown to blackish brown, lightly pruinose asci: cylindrical to subclavate, 8-spored ascospores: brown, l-septate, ellipsoid, Pachysporaria-type, 40-45 x 20-22 µm Pycnidia: rare, immersed conidia: bacilliform, 4-5 x 1 µm Spot tests: cortex K+ yellow C-, KC-, P+ yellow; medulla K+ yellow or K+ yellow to orange, C-, KC-, P- or P+ yellow to orange Secondary metabolites: cortex with atranorin and chloroatranorin; medulla with atranorin, zeorin, ± norstictic acid, ± salazinic acid and unidentified terpenes. Substrate and ecology: growing on tree trunks or over mosses on rocks in both open and shady situations World distribution: pantropical to subtropical species extending to warm temperate regions Sonoran distribution: probably the most common Heterodermia in the region, occurring in the mountains of Arizona and the Sierra Madre Occidental region of Chihuahua and Sinaloa and in the higher mountains of Baja California and Baja California Sur. Notes: It is characterized by the dull upper surface, ± fan-like lobe apices, the absence of a lower cortex and by having a white to blackish-violet lower surface. This is however an exceedingly variable species in both morphology and chemistry. The lobes may become more elongate in shady habitats when they may have distinct long, black marginal rhizines (to 7 mm). The soredia may vary from farinose to granular or may be virtually lacking. Swinscow and Krog (1976a) document a similar variation in East Africa. The sparse brownish orange-red pigment pr esent on the lower lobe apices should not be confused with the more distinct, continuous pigmented lower surface of H. obscurata. Heterodermia dendritica var. propagulifera was already discussed and regarded as a modification of H. japonica by Swinscow and Krog (1976a, p. 133) and they have examined the holotype in TUR and the isotype in BM. We fully agree with their conclusions and thus formalize the synonymization.