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 Thallus: orbicular or irregular, up to 4 cm diam., sometimes confluent with other thalli, loosely adnate; lobes: radiating, truncate with open sinuses, up to 1 mm wide but mostly c. 0.5 mm, eciliate; upper surface: whitish gray to cream-colored (margin often paler), mostly without pruina and maculation; soredia and isidia absent; upper cortex: paraplectenchymatous; medulla: white; lower cortex: prosoplectenchymatous, cells sometimes short and thick-walled; lower surface: white to brownish, with few pale rhizines; Apothecia: usually abundant, variable in size, up to 1.5 mm diam., but usually less than 1 mm; margins: thick; disc: often pruinose; ascospores: brown, 1-septate, Physcia- or Pachysporaria-type, (14-) 17.5-22.5 (-28) x (6.5-) 8-10 (-12) µm; Pycnidia: ± abundant; conidia: subcylindrical, 4-6 x 1 µm; Spot tests: cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C-, KC-, P-; Secondary metabolite: upper cortex with atranorin.; Substrate and ecology: growing on trees in open situations; World distribution: widely distributed species within the arctic, boreal and temperate vegetation zones; Sonoran distribution: a relatively frequent species on trees from low to upper montane localities of Arizona, southern California, Baja California, Baja California Sur, and Sonora.; Notes: The abundant apothecia, the K– medulla and corticolous habitat are the main characters of P. stellaris. There is a slight difference in morphology and appearance within the range of its distribution (Moberg 1986: 860) and the Sonoran Desert material is closer to the southern type as would be expected. The closely related species P. convexella differs in lobe shape and substrate preference. 


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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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