Thallus: subfruticose, consisting of upright, elongate squamiform or subcylindrical lobes forming cushions up to 2 cm wide (or larger aggregates) lobes: bifacial, tortuose nodulate, ± stipitate, up to 7 mm tall, 0.15-0.3 mm thick, repeatedly dichotomously branched, several of them rising from a common holdfast upper surface: medium to dark brown or brown-black, dull upper cortex: 20-30 µm thick, composed of roundish-angular cells (4-8 µm in diam.), lacking an amorphous layer medulla: white, loosely filamentous with large air spaces especially in nodular parts of lobes, hyphae c. 3 µm thick; algal layer: 50-100 mm high, uneven above and below, horizontally discontinuous; algal cells: c. 7-9 µm in diam., interstitial hyphae paraplectenchymatous above, rather loosely arranged below lower cortex: abruptly delimited, paraplectenchymatous, 25-45 µm thick, hyaline to pale brownish, composed of rather thick-walled, conglutinated, angular cells (5-10 µm wide) in distinct vertical columns; rhizohyphae: lacking lower surface: paler than upper side, rugose, bare; squamules attached by holdfasts Perithecia: innate in distal parts of lobes, causing swellings on the underside, broadly pyriform, up to 0.3 mm wide; exciple colorless or very pale brownish; periphyses: 50-80 µm long; hymenial algal cells: ellipsoid-oblong to mostly elongate, 5-8 x 2.5-3 µm, up to 12 µm long when in division asci: narrowly clavate, c. 100-130 x 25-33 µm, 2-spored ascospores: strongly muriform, at first hyaline but becoming dark brown with age, 45-57 x 21-25/ 45-60 x 13-20 µm (distal/proximal spores) Pycnidia: not seen Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on calcareous or non-calcareous rocks World distribution: mainly northern, scattered in North America, Greenland, Scandinavia Sonoran distribution: collected only once in the Sierra San Pedro Martir at 2800 m in Baja California. Notes: Endocarpon pulvinatum is unique in being subfruticose, in the construction of its lower cortex of strictly vertically arranged hyphae, and in having elongate hymenial algal cells.