Thallus: crustose, forming patches from 5-10 mm to several cm in diam., without a prothallus or distinct edge, sometimes occurring as a lumpy granular film, inconspicuous when dry except around emergent apothecia, gelatinous and easily mistaken for algal scum, often completely immersed in upper layer of sediment with fine particles and causing it to crack when dry into plates surface: dull white or dirty ochre when dry, green when wet internal structure: heteromerous but with indistinct layers, with inconspicuous, prosoplectenchymatous phenocortex, becoming gelatinized around soil particles especially under apothecia; secondary propagules: absent Apothecia: round to slightly irregular, usually immersed-erumpent but almost sessile when old, with concolorous proper margin and a raised, irregular, lacerated, sometimes evanescent thalline rim, irregular, somewhat knobby or flexuous, mostly c. 0.5 mm wide but sometimes up to 1.5 mm across; abundant but widely scattered, emergent from the soil or visible granules of thallus disc: black, brown when moist often with faint reddish center, dull, plane to slightly convex exciple: distinct, dark brown to almost black, subparaplectenchymatous but lumina indistinct in water epihymenium: dark brown, conglutinate, less than 10 µm thick hymenium: pale brown to yellow, conglutinate, 70-100(-120) µm tall; paraphyses: thin and indistinct subhymenium: hyaline or pale yellow, c. 15 µm thick; hypothecium: hyaline or pale yellow, indistinct from subhymenium, thin beneath apothecium, widening and radiating upward into margin asci: clavate, 70-80 x 20-25 µm, usually 4- or 5-spored ascospores: hyaline, submuriform, 25-30(-40) µm x 15-20 µm, 8-12 cells Hyphophores: not observed Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on soil, fine-grained sediment, sand or sandy clay, forming soil crust associated with scattered mosses, Psora species, and cyanobacteria World distribution: southern and central Europe (Corsica, France, Czech Republic, and Portugal), South Africa, and southern California Sonoran distribution: Los Angeles County, southern California (historic collections from Santa Monica Mountains and Verdugo Mountains by Hasse). Notes: The collections from southern California, designated as Rhizocarpon athalloides by Has-se (1913), match the type and the European collections of Diploschistella athalloides rather well and are here identified with that name. Vězda (1972) already cited a Hasse collection, which was also seen by us (Santa Monica range, 1896, Lichens of Southern California no. 788, NY, herb Vězda ), when making the combination G. athalloides, and there is a specimen in H-Nyl labeled "L. athalloides Nyl. = L. psammoica Nyl. California Hasse" that was annotated by Vězda in 1963 as Lopadium athalloides (Nyl.) Samp. (R. Skytén, pers. comm.). Diploschistella athalloides at first glance resembles species of Diploschistes, from which it is distinguished by its thin, inconspicuous thallus, thin anastomosing paraphyses and hyaline, thin-walled ascospores. Gyalidea (Solorinella) astericus is also very similar in morphology and ecology but has very conspicuous thalline lobes around the apothecia, unbranched paraphyses, and numerous transversely septate ascospores per ascus. Diploschistella athalloides might be confused with Gyalideopsis mexicana, but the latter has broadly sessile to applanate apothecia without thalline rim and setiform, capitate hyphophores and grows over bryophytes and detritus. Ecologically, Diploschistella athalloides seems adapted to soil that is regularly, but gently, disturbed by the deposition of fine layers of sediment, low in nutrition for vascular plants, probably in full sun, and with weak competition from mosses and other soil lichens; for example, thin-soiled openings in chaparral and coastal sage scrub with low seasonal flushing of nutrients. No collections of this species in southern California have been documented since Hasse, but it is an inconspicuous species that would be hard to find unless one were looking carefully for its apothecia.