Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Life habit: lichenized Thallus: foliose and rosette-forming, or subfruticose and caespitose, loosely adnate to loosely attached lobes: somewhat elongate, averaging to 2-7 (-10) mm wide, moderately thick, usually dorsiventral with raised tips (or terete in one Eurasian species), flat and canaliculate or terete, adnate or raised; marginal projections: present or absent; cilia absent upper surface: bright to dark yellow, greenish yellow, or almost grayish green, often wrinkled or ± folded, continuous; with or without soredia; isidia and pseudocyphellae absent upper cortex: paraplectenchymatous, with 3-5 layers of pachydermatous cells; uppermost cells: isodiametric, 3-5 µm diam.; cells of the two lower layers: usually elongated, 5-6 x 2-3 µm, sometimes isodiametric; parts of upper cortex exposed to the sun with usnic acid crystals; epicortex: usually non-pored, smooth and thin, c. 1 µm, brown in some non-Sonoran species medulla: bright yellow, 20-30 µm thick; hyphae 3-5 µm thick, surface smooth; cell walls: containing Cetraria-type lichenan, I+ blue photobiont: primary one a trebouxioid alga, secondary photobiont absent; spherical, 3-15 µm diam., in a layer 10-30 µm thick; algae more abundant in young and more exposed parts of the thallus lower cortex: ± similar to upper one but often less inspersed lower surface: pale yellow to whitish, central parts black in some species, rhizinate; rhizines: laminal, pale to black, rather sparse, rarely close to the margin, simple or irregularly branched Apothecia: submarginal or laminal, sessile, roundish; disc: brown, imperforate; thalline margin: prominent, often crenulate; exciple: gray, hyaline, or yellow; hymenium: hyaline below and brown above, with blue IKI reaction in lower part (0.3% iodine solution); paraphyses: not (or scarcely) branched and anastomosing; hypothecium: hyaline asci: Lecanora-type s.l. (Melanelia-type), broadly to very broadly clavate, 30-40 x 10-15 µm; tholus: well-developed, c. 10 µm high, with moderate to very strong IKI reaction (0.03% iodine solution), with wide ocular chamber and large (4 x 2 µm) axial body; 8-spored ascospores: simple, hyaline, spherical to subspherical or broadly ellipsoid, c. 4-6 (-7) x (3-) 4-5 (-6) µm, obtuse at the poles, without distinct endospore thickening, not amyloid Pycnidia: often abundant (but rare or absent in some species), usually on marginal or occasionally laminal projections, 80-170 x 70-120 µm, immersed or emergent and sessile or stalked, generally conspicuous, wall at least partly with black pigment conidia: formed acrogenously, sublageniform, 6-8 x 1-2 µm or citriform, 3-4 x 1-2 µm Secondary metabolites: usnic acid, pulvinic acid derivatives, terpenoids or fatty acids Geography: arctic to boreal or temperate, Northern Hemisphere Substrate: on bark, wood, soil, detritus, or rock (calciferous or not). Notes: Vulpicida is a segregate from Cetraria and is distinguished by the distinctly yellow color of the thallus caused by pulvinic acid derivatives in the medulla and usnic acid in the cortex, smooth medullary hyphae, ± globose ascospores, and the absence of cilia and pseudocyphellae. The other yellowish species formerly placed in Cetraria or its segregate Tuckermannopsis but now placed in other genera have usnic acid but lack pulvinic acid derivatives. Other characters used to distinguish Vulpicida from similar genera are the moderately sized asci with often very strong amyloid reaction in the tholus, the strongly gelatinized lower layer of the exciple, the small cortical cells, and the lageniform to citriform conidia. Morphologically the genus is most similar to Tuckermannopsis, but differs in the shape of the asci and conidia. Some of the information presented below on external morphological characters in the individual species (especially colors and dimensions) is based primarily on observations of material from the Sonoran region.