Thallus: irregular to orbicular, up to 10 cm diam., dichotomously lobate lobes: long, linear, distinctly separate and spreading, up to 1 mm broad, ciliate; cilia: prominent, marginal, up to 7 mm long, giving the margin a comblike appearance upper surface: gray to whitish gray; soredia and isidia absent upper cortex: prosoplectenchymatous medulla: white, forming lowermost part of lobes lower cortex: absent lower surface: white, sometimes bluish, erhizinate Apothecia: laminal and/or terminal, short stipitate, up to 5 mm in diam. with shortly lobulate margin often folded over the hymenium asci: subclavate to clavate, 8-spored ascospores: brown, l-septate, ellipsoid, Pachysporaria-type, sometimes with sporoblastidia, (29-) 32.5-38.5 (-42) x (14-) 15-18 (-21.5) µm Pycnidia: common, immersed, appearing as distinct, black warts on the upper side conidia: bacilliform, 4-6 x 1 µm Spot tests: cortex K+ yellow C-, KC-, P+ yellow; medulla K+ yellow, C-, KC-, P- Secondary metabolites: cortex with atranorin and chloroatranorin; medulla with atranorin and zeorin. Substrate and ecology: grows abundantly on tree trunks in oak woodland and seems to prefer open localities in fairly humid areas World and Sonoran distribution: Sinaloa and mountains in southern Baja California Sur between 1200 and 1800 m. Notes: The publication of this species as H. lineare was orthographically incorrect and is hereby emended to H. linearis. Heterodermia linearis is a robust species recognized by the linear lobes with regularly ciliate margins and abundant apothecia and pycnidia. It differs from H. leucomela by the absence of soralia and from fertile H. leucomela by the abundant pycnidia and entire or only shortly lobulate apothecial margins.