Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: crustose, continuous or rimose-areolate or verrucose-areolate; prothallus: blackish to bluish brown areoles: flat or verrucose or verruculose, thin, ecorticate surface: yellowish white to yellowish gray or yellowish green, smooth, opaque, epruinose, with an indistinct margin, +sorediate soredia: granulose, 25-35 µm in diam, in well defined, white to whitish gray soralia 0.1-0.3 mm in diam. Apothecia: subimmersed when young, sessile when mature or sessile, 0.4-1 mm in diam., lecanorine disc: orange-brown or yellowish brown, plane, epruinose margin: concolorous with thallus, thin or thick, persistent, even, not flexuose, smooth, entire or verrucose or verruculose, without a parathecial ring amphithecium: present, with numerous algal cells, with large crystals insoluble in K, corticate; cortex: hyaline, indistinct, basally not thickened, gelatinous or interspersed, (10-)15-25 µm thick laterally, (10-)15-20(-25) µm thick basally parathecium: hyaline, containing crystals insoluble in K epihymenium: red-brown to orange-brown, with pigment dissolving in K, with crystals dissolving in K hymenium: hyaline, clear; paraphyses: not thickened (up to 2 µm wide) apically, not pigmented; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, (8-)8.511.5(-14) x (4-)4.5-5.5(-7) µm; wall: less than 1 µm thick Pycnidia: immersed, cerebriform; conidiophores: type II sensu Vobis conidia: filiform, (14-)15-18 µm long Spot test: thallus and apothecial margin K+ yellow, C-, KC-, P+ pale orange Secondary metabolites: arthothelin (minor), atranorin (major), chloroatranorin (minor), 2'-O-methylisohyperlatolic acid (trace), 2'-O-methylperlatolic acid (major) and 2'-O-methylsuperlatolic (trace). Substrate and ecology: on bark of deciduous trees World distribution: pantropical occurring in Africa, Australasia, Central and South America, and the Pacific Area Sonoran distribution: Baja California, Baja California Sur, and Sinaloa. Notes: Lecanora helva is characterized by the small orange to pale brown apothecial discs, the nature of the epihymenium and amphithecium, and the thallus chemistry. Morphologically it is similar to L. achroa and L. leprosa. However, those two species can be readily distinguished from L. helva by their different chemistry; moreover, L. achroa has slightly larger ascospores while L. leprosa generally has a thicker, pale green thallus with a smoother surface.