Thallus: areolate to squamulose, sometimes ±continuous and rimose, 2-4 cm in diam., (0.2-)0.4-1(-1.5) mm thick areoles: ±squamule-like, angular to irregular, flat, sometimes concave or uneven, (0.3-)0.7-1.6(-2.5) mm in diam., contiguous prothallus: absent surface: buff to light brown or ochre, dull to slightly shiny upper cortex: 30-40(-50) µm thick, uppermost part indistinctly light brown, 5-10 µm thick, with cells 5-7 µm in diam.; cortex covered with an epinecral layer or with crystals, 10-20(-40) µm thick photobiont: chlorococcoid, 5-17 µm in diam. Apothecia: aspicilioid, rather common, (0.1-)0.3-0.9(-1.3) mm in diam., 1-2(-5) per areole, round, rarely angular or elongated, when mature sometimes almost sessile disc: black to brown-black, plane or sometimes concave, usually with a thin, white pruina thalline margin: elevated when mature, sometimes prominent, ±crenulate, usually forming a white rim exciple: (25-)30-100(-140) µm wide, I-; uppermost cells brown, ±globose, (3-)4-5 µm in diam. epihymenium: olive to olive-brown or brown, with crystals, N+ green to blue-green, K+ brown hymenium: hyaline, I+ persistently blue, 100-150(-160) µm tall paraphyses: submoniliform, with (0-)1-2(-3) upper cells ±globose to subglobose or sometimes subcylindrical to cylindrical, 2-4(-5) µm wide, in lower part 1-1.5(-2) µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue or partly turning yellow-green, together 20-40(-50) µm thick asci: clavate, 70-90 x 22-32 µm, (2-)3-6-spored ascospores: globose to subglobose, hyaline, simple, (16-)18-23(-27) x 15-21 µm Pycnidia: uncommon, 1(-3) per areole, immersed, (100-)130-250 µm in diam., with a black, punctiform ostiole, sometimes surrounded by a white rim, 60-100(-150) µm in diam. conidia: filiform, straight or slightly curved, 7-11(-12) x 0.6-0.8(-1) µm Spot tests: cortex and medulla I-, K-, P-, C- Secondary metabolites: aspicilin. Substrate and ecology: on clay, soil and disintegrated granite World and Sonoran distribution: southern California: Los Angeles Co. (Santa Monica Mountains and San Clemente Island) and Santa Barbara Co. (Santa Rosa Island), at 270-360 m. Notes: Aspicilia praecrenata is characterized by a ±squamulose, buff to light brown thallus, growing on soil or disintegrated granite, and apothecia with a ±crenulate, often white, thalline margin. Furthermore, the paraphyses are submoniliform, the asci contain 2-6 globose spores, the conidia are short and it contains aspicilin. Additional, potential material on rocks, collected in Santa Monica Mountains (Knudsen 4364.2) and Sonora in Mexico (Ryan 21639) is habitually similar and might also belong to A. praecrenata, but this should be confirmed by DNA-studies. Another species growing on soil or disintegrated granite and occurring in the same area as A. praecrenata is A. glaucopsina. This species, however, has asci with 8 ellipsoid spores and longer conidia. Some terricolous specimens collected in Riverside County (Knudsen 371, 372 & 398) have an areolate to rimose or almost continuous thallus with an olive-brown to dark brown color. The apothecia lack pruina, the thalline margin often has a white rim but is not crenulate. The asci contain 2-4 globose spores and the conidia are short. Another specimen from Ventura County (Owe-Larsson 9101) with these characters but with a brown areolate thallus grows on rock. Two of the specimens (Knudsen 371 & Owe-Larsson 9101) have been analyzed for DNA (ITS) and they show close similarity. These specimens, which all lack aspicilin, might represent an undescribed species, but DNA from A. praecrenata should be analyzed before this can be settled.