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Placidium californicum Breuss
Family: Verrucariaceae
Placidium californicum image
Thallus: squamulose squamules: c. 2-4 mm wide and 0.35 mm thick, fully appressed, roundish or slightly lobed, ± dispersed or a few adjacent upper surface: brown, dull upper cortex: c. 30-60 µm thick, epinecral layer almost lacking or up to 20 µm thick medulla: white, usually with numerous globose cells (c. 9-14 µm in diam.); algal layer: c. 70-100 µm high lower cortex: absent or at least lacking distinctive development lower surface: brownish; rhizohyphae: hyaline, rather thin (3.5-4.5 µm) Perithecia: broadly pyriform to subglobose, up to 0.45 mm wide, with colorless wall asci: cylindrical, 70-80 x 13-17 µm, 8-spored ascospores: uniseriate, subglobose or broadly ellipsoid, 10-13 (-15) x (7.5-) 8-9 (-10) µm, rather thick-walled Pycnidia: not seen Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: soil, in open places, mostly coastal World distribution: endemic to SW North America Sonoran distribution: on coastal sites of southern California and Baja California. Notes: The species very much resembles P. squamulosum, but differs in its almost spherical and thick-walled spores and in having thinner rhizohyphae.