Thallus: foliose, very firmly appressed, up to 6 cm in diam. lobes: flat, rarely slightly concave, 0.2-0.3 mm wide upper surface: light gray or leaden, older thalli olivaceous to brownish gray; pseudocyphellae: sparse, usually restricted to the margins of peripheral parts of the lobes, rarely reticulately confluent; pruina: hardly visible; soralia, isidia and polysidiangia lacking medulla: upper part light orange, lower part white or white throughout lower surface: black in center, paler towards lobe tips; rhizines: ± sparce, blackish, furcately divided Apothecia: obscurascens-type, often present, laminal, 0.25-0.6 mm wide; disc: black, not pruinose internal stipe: indistinct, upper part creamish yellow or white, lower part white ascospores: one-septate, brown, 13-17 x 4.5-7 µm (length-width-index: 2.2-3.2) Pycnidia: immersed conidia: bacilliform, 3-4 x 1 µm Spot tests: upper cortex K-, C-, KC-, P-; medulla upper and lower part K-, C-, KC-, P- or P+ orange-red caused by testacein; internal stipe upper part K-, C-, KC-, P-; lower part K-, C-, KC-, P- Secondary metabolites: upper cortex with lichexanthone; medulla with terpenes of a characteristic array on TLC plates, with or without testacein (the latter present in all Sonoran collections). Substrate and ecology: on acidic rocks in montane areas World distribution: neotropical Sonoran distribution: Baja California Sur and Sonora in tropical thorn forest to deciduous forest transition areas. Notes: The difficulty of distinguishing P. microspora and P. pyxinoides has been mentioned by several authors (Swinscow and Krog 1975, Awasthi 1982, Kalb 1987), but spore dimensions (length-width-index: 2.2-3.2 in P. pyxinoides and 1.6-2.4 in P. microspora) are definitive. In addition, TLC results also helps to assign the correct species name to a collection. It cannot, however, be unequivocally concluded that only two species are involved in this difficult group. The presence or absence of testacein probably is of no taxonomic value, as has been demonstrated for Parmelia testacea (Elix 1994h).