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: tightly to loosely adnate, foliose, often dichotomously lobate lobes: usually sublinear, sometimes subirregular or linear-elongate, sometimes imbricate; axils: sinuous or V-shaped; lobe tips: usually subtruncate, but sometimes rounded, incised or not, cilia absent or rarely short ciliate upper surface: gray, ivory or yellow green, smooth, plane to rugulose, shiny or dull, sometimes white maculate, usually epruinose, pseudocyphellae absent upper cortex: pored epicortex, palisade paraplectenchymatous medulla: white or rarely partially yellow or orange, cell walls containing isolichenan photobiont: primary one a Trebouxia, secondary photobiont absent lower surface: black, sometimes with brown tips, plane to sometimes wrinked, rarely subcanaliculate, attachment by dichotomous rhizoid holdfasts, without cyphellae, pseudocyphellae or tomentum Ascomata: apothecial, imperforate, laminal, orbicular, cup-shaped, sessile or subpedicellate; margin: prominent with thalloid rim; exciple: gray or hyaline; epithecium: brown or brownish yellow; hypothecium: hyaline asci: lecanoral, apex I+ blue, with wide, axial body divergent towards apex, 8-spored ascospores: simple, ellipsoid to broadly ellipsoid; wall: thin, hyaline Conidiomata: pycnidial, laminal to marginal, immersed conidia: bacilliform or weakly bifusiform, 5-8 x 1 µm Secondary metabolites: upper cortex with either atranorin and chloroatranorin (gray), lichexanthone (ivory), or usnic acid (yellow-green); medulla with some combination of orcinol depsides, orcinol depsidones, ß-orcinol depsides, ß-orcinol depsidones, (higher) aliphatic acids, rarely triterpenoids, anthraquinones, xanthones, and dibenzofurans Geography: predominantly tropical, montane to subalpine, but some species also occurring in temperate areas (particularly in maritime influenced regions) Substrate: mostly on bark or acidic rocks, rarely on compacted soil. Notes: Although all the species in the Sonoran region are gray and have atranorin or rarely lichexanthone or isousnic acid in the upper cortex, there are a few yellow species, particularly in the tropics, with usnic acid in the upper cortex. Previously Hypotrachyna was treated as a section of Parmelia by Vainio (1890) and later raised to a subgenus (Hale and Kurokawa 1964). As it became clear that this large, predominately tropical group of lichens was quite different from the temperate to arctic Parmelia s.s, it was finally raised to the genus level (Hale 1974a), a status that is widely recognized today. Key characters for the genus include subtruncate lobe apices, lack of marginal cilia, dichotomously branched rhizines and bifusiform conidia.