Thallus: squamulose squamules: adjacent or slightly overlapping, 2-3 mm wide, 0.2-0.25 mm thick, adnate, the margins free from the substrate and slightly elevated, rounded to irregularly lobed upper surface: pale brown, gray-brown or beige, smooth, dull cortex: lacking, lowermost part of squamules composed of more tightly packed medullary hyphae (some of them bending into the substrate as rhizohyphae); rhizohyphae: hyaline, c. 2.5 µm in diam.; 20-40 µm thick, composed of angular cells (5-9 µm wide in upper part, their size continuously enlarging with depth up to 16 µm in diam.) medulla: composed of loosely interwoven, filamentous hyphae with a few spherical cells (in lowermost parts more tightly packed without forming a true cortex); algal layer: averaging 70 µm in height; algal cells: 7-14 µm in diam. lower surface: whitish to pale brown Perithecia: broadly pyriform to subglobose, up to 0.3 mm wide, perithecial apex concolorous with thallus or slightly darker, inconspicuous; exciple: brown to black, c. 30 µm thick; periphyses: c. 30-40 µm long; hymenial algal cells: globose, 3-5 µm in diam. asci: clavate to cylindroclavate, 75-95 x 20-25 µm, 2-spored ascospores: hyaline to slightly brownish, muriform, broadly ellipsoid to elongate, 28-34 x 13-16/ 30-40 x 11-13 µm (proximal/distal spores) Pycnidia: inconspicuous, small conidia: shortly bacilliform, 3-5 x <1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: mainly on soil, rarely on rock or bark in dry regions; the Mexican specimen was collected from a tree trunk World distribution: central and southern Europe, N Africa, United States and Australia Sonoran distribution: southern California and Sonora. Notes: Endocarpon pallidum can be readily recognized by its loosely filamentous medullary tissue.