Thallus: squamulose squamules: scattered to contiguous but hardly overlapping, c. 1-3 mm wide, 0.15-0.25 mm thick, usually weakly to deeply lobate, plane and fully adnate, more rarely concave with margins turned upward, with conspicuous black rhizines anchoring and linking squamules upper surface: pale ochraceous brown to dark brown or with an olivaceous tinge or red-brown, smooth, dull upper cortex: 30-70 µm thick, composed of angular cells (5-10 µm in diam.), in ± distinct vertical rows, isodiametrical or vertically elongated, composed of equal sizes throughout or becoming somewhat larger (up to 12 µm) with depth, overlain by a thin to thick amorphous layer medulla: white, subparaplectenchymatous, composed of roundish cells (5-10 µm in diam.); algal layer: c. 50-80 µm high, unevenly delimited below, horizontally continuous; interstitial hyphae: paraplectenchymatous; algal cells: 6-10 µm in diam., in vertical rows lower cortex: brown-black, ± paraplectenchymatous in upper part, merging into a ± thick, dark basal layer composed of interwoven hyphae interspersed with substrate particles; rhizohyphae: hyaline to brown lower surface: black, rhizinate; rhizines: usually conspicuous, moderately to richly branched, black, with a carbonaceous envelop and a white core, with main stems up to 0.25 mm thick and up to several mm long; ramifications: partly anastomosing thus linking squamules Perithecia: (sub-) globose, up to 0.4 mm wide; exciple: brown-black to black, 20-30 µm thick; periphyses: 40-60 µm long, simple; hymenial algal cells: subglobose and (2.5-) 3-4 (-5) µm wide to ellipsoid-oblong and 4-6 (-7) x 2.5-3 (-4) µm asci: clavate to cylindro-clavate, 90-125 x 20-33 µm, 2-spored (very rarely 1-spored) ascospores: muriform, hyaline to dark brown, broadly ellipsoid to elongate-ellipsoid to subcylindrical, 35-53 (-60) x 16-26/40-65 x 13-18 µm (distal/proximal spores) Pycnidia: immersed, up to 0.2 mm wide, opening indistinct or crateriform conidia: bacilliform, 3-5 x <1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on bare or mossy soil and soil cover over rocks, rarely on crumbling rock, over both calcareous and non-calcareous substrate, from low to high elevations World distribution: cosmopolitan Sonoran distribution: common but never abundant in Arizona, California, Baja California, Baja California Sur, Chihuahua and Sonora. Notes: Endocarpon pusillum is quite variable considering thallus morphology, development of upper cortex, thickness of the dark basal layer, and ascospore size and pigmentation. Black rhizines, a black basal layer and bisporous asci is the diagnostic combination of characters. The rhizines are usually conspicuous, but may be stubby in poorly developed thalli or thalli growing directly on (crumbling) rock. These specimens are easily confused with Endocarpon pseudosubnitescens auct. (see under that species). Specimens of Endocarpon loscosii with unusual dark undersides and rhizines can easily be distinguished by their notably shorter asci (75-95 x 20-28 µm as against to 90-125 x 20-33 µm in E. pusillum). The type material of both Endocarpon lepidallum and E. subnitescens agrees in all aspects with E. pusillum and is therefore reduced to synonymy.