Thallus: foliose, orbicular to irregular, small, usually less than 4 cm diam., loosely adnate, densely dichotomously lobate lobes: long and narrow, up to 1 (-1.5)mm broad, repeatedly branched, weakly convex, widening, the tips not ascending, minutely notched, eciliate upper surface: grayish white to gray to brownish gray, darker at lobe tips, sometimes weakly pruinose; sorediate soredia: white to bluish gray, in semi-capitate soralia, sometimes at lobe-tips but mainly arising from small lateral knob-like structures upper cortex: prosoplectenchymatous medulla: white lower cortex: prosoplectenchymatous lower surface: whitish to pale brown, rarely dark gray; rhizines: weakly developed, usually short (c. 1 mm), pale to dark brown or black Apothecia: rare (not seen in Sonoran material), subsessile, 1-3 mm in diam., margin sorediate; disc: brown to blackish brown, epruinose asci: cylindrical to subclavate, 8-spored ascospores: brown, l-septate, ellipsoid, 26-32 x 12-14 Pycnidia: ± common, immersed conidia: bacilliform, 4-5 x 1 µm Spot tests: cortex K+ yellow C-, KC-, P+ yellow; medulla K+ yellow to orange, C-, KC-, P+ yellow to orange Secondary metabolites: cortex with atranorin and chloroatranorin; medulla with atranorin, zeorin and an unidentified terpenes (accessory) and norstictic acid (major) and connorstictic acid (minor). Substrate and ecology: growing mainly on rocks, more rarely on trees in open but humid situations World distribution: eastern North America and scattered localities on all continents Sonoran distribution: Arizona and several in Chihuahua in the Sierra Madre Occidental. Notes: This species is characterized by the narrow, convex, long lobes, corticate on the lower surface. The soralia arise mainly from marginal knob-like structures forming small, semi-capitate soralia. The records of salazinic acid are probably misinterpretations of connorstictic acid which seems to be regularly present. The type material does not contain salazinic acid (Swinscow and Krog 1976), and our collections from southeastern U.S.A. also lack salazinic acid, which agrees with Culberson (1966). The K+ reaction is similar to that of H. albicans (with salazinic acid), which also has similar soralia. However, the soralia of H. albicans are ± continuously marginal, and it is more firmly adnate and does not contain norstictic acid. Heterodermia speciosa is usually larger, has ± flat lobes and lacks both norstictic and salazinic acid.