in Nash III & al. (eds.) Lichen Flora of the Greater Sonoran Desert Region, 2: 328, 2004
Description: Thallus crustose to subsquamulose and then resembling a cushion of Cladonia-squamules, subleprose, forming effigurate to subplacodioid, well-delimited, up to 2 cm wide rosettes with crisped margins, the marginal lobes up to 2(-3) mm wide and 0.3-1 mm thick, with rounded apices and usually raised, up to 0.5 mm thick margins, the rosettes often confluent into a coarse, irregularly spreading, up to 1 dm wide crust. Upper surface whitish grey to pale yellowish grey, with numerous horizontal to vertical, fragile, easily detached, flattened to more or less globular, 0.1-0.4 mm wide, discrete lobules which are initially ecorticate, but soon develop a thick pseudocortex, not forming compound units; soredia-like granules few or absent; medulla distinct in thick specimens, white, the hyphae heavily encrusted with crystals visible under polarized light; hypothallus compact, composed of tightly intertwined hyphae. Photobiont chlorococcoid. Spot tests: K+ yellowish, C-, KC-, P+ yellowish, UV-. Chemistry: two chemotypes: 1) atranorin, pannaric 6-methylester, roccellic/angardianic acid and/or rangiformic/jackinic acid, 2) (not known from Europe) norascomatic acid (major), strepsilin, isostrepsilic acid, atranorin and chloroatranorin (minor).
Note: a recently-described species, common in California and Baja California, apparently rare in Europe, being only known from Spain; it grows on dry soil, rarely on bare rock in open, Mediterranean to semi-desert vegetation, on surfaces wetted by rain. To be looked for in the driest parts of Mediterranean Italy.
Growth form: Leprose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by isidia, or isidia-like structures (e.g. schizidia)
USA, California, Santa Monica Mountains, on soil [Hollinger 4242] - 2011-10-19. Herbarium: Holotype Source: https://www.waysofenlichenment.net/lichens/Lepraria//Taxbrowser_Taxonpage?taxid=783022/Arthonia_byssacea_l2.jpg