Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: rimose to areolate, 2-5.5 cm in diam., (0.1-)0.2-0.5(-0.7) mm thick areoles: angular to sometimes rounded, flat to slightly convex, at the thallus edge sometimes extended, (0.2-)0.4-0.9(-1.3) mm in diam., contiguous prothallus: often present at the thallus edge as a ±continuous zone or sometimes fimbriate, (0.1-)0.5-1 mm wide, brown-black, blue-black, olive-black or black, outermost part white surface: brown to ochre with an ±olive tinge, dull or slightly shiny cortex: (15-)20-40(-45) µm thick, uppermost part brown, 10-15(-25) µm thick, cells 5-7(-8) µm in diam.; cortex covered with an epinecral layer 2-10 µm thick photobiont: chlorococcoid, cells ±round, 5-15 µm in diam. Apothecia: aspicilioid, numerous in the middle of the thallus, small, 0.1-0.4 mm in diam., 1-2(-3) per areole, ±round disc: black, usually without pruina, rarely with a thin, white pruina, concave to flat thalline margin: flat to slightly elevated, concolorous with thallus or sometimes with a white rim, or sometimes darker than thallus exciple: 30-40(-50) µm wide, I-; uppermost cells brown, ±globose, (4-)5-6(-7) µm in diam. epihymenium: dark olive to olive-brown or brown, without or with a few crystals, rarely with numerous crystals, N+ green, K+ brown hymenium: hyaline, I± persistently blue or partly turning yellow, (120-)170-220 µm tall paraphyses: moniliform, with (2-)3-5 upper cells ±globose, 4-5 µm wide, in lower part 1.5-2 µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I± persistently blue or partly turning yellow, overall (40-)50-90 µm asci: clavate, 80-130 x 21-32 µm, 8-spored ascospores: hyaline, simple, ellipsoid to sometimes subglobose, (16-)18-26 x (10-)11-16(-18) µm Pycnidia: immersed, rather often present, 1-2(-4) per areole, (100-)120-180 µm in diam., with a black, punctiform, often somewhat elevated ostiole, 50-100(-120) µm in diam. conidia: filiform, straight or slightly curved, (8-)10-15(-18) x 0.8-1 µm Spot tests: cortex and medulla I-, K-, P-, C- Secondary metabolites: none detected by TLC. Substrate and ecology: on wood (2 specimens) on Cupressus guadalupensis in open Cupressus forest or on basaltic rock (2 specimens) in open grassland or Cupressus forest, altitude 720-1250 m World and Sonoran distribution: Endemic on Guadalupe Island (Mexico, Baja California). Notes: Aspicilia guadalupensis is known from four collections from Guadalupe Island. The species is characterized by its brown to ochre thallus color with an olive tinge, an evident dark prothallus with a white outer margin, small apothecia, tall hymenium, large spores and rather short to medium sized conidia. Aspicilia phaea, found in California, is microscopically quite similar to A. guadalupensis, but differs by its brown to gray-brown thallus color without an olive tinge, a less developed prothallus which lacks a white outer margin, larger apothecia and somewhat shorter conidia.