Physcia crispa  

 Thallus: irregular to orbicular, thin, rarely exceeding 150 µm thick, up to 3 cm across or larger because of confluent thalli; lobes: loosely adnate, up to 1 mm wide, rarely broader, about the same in length; lobe tips ascending and usually crenulate, with small protrusions along the margin becoming isidia-like and eventually forming soredia, eciliate; upper surface: gray to cream colored, rarely with a pruina, sorediate; soredia: in marginal soralia, well developed in inner parts, particularly at the lobe angles; upper cortex: paraplectenchymatous; medulla: white; lower cortex: paraplectenchymatous; lower surface: whitish with a few pale rhizines; Apothecia: sometimes present, up to 2 mm diam.; margins: with sorediate; disc: pale brown to brown, not pruinose; ascospores: brown, 1-septate, Pachysporaria-type, (18-) 20-25 (-27) x (8-) 9-11 (-13) µm; Pycnidia: rare; Spot tests: upper cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C-, KC-, P-; Secondary metabolite: upper cortex with atranorin.; Substrate and ecology: at the only known locality growing on trees at 500 m; World distribution: South America, East Africa and SW North America; Sonoran distribution: only one locality in Baja California Sur in the Sierra de La Laguna.; Notes: The thin often undulating thallus, the K- medulla and the paraplectenchymatous lower cortex are the main characters. Physcia crispa may have some similarities to P. undulata but in the latter species the medulla reacts K+ yellow and the lower cortex is prosoplectenchymatous.