Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Fissurina humilis: (Vain.) Staiger, Biblioth. Lichenol. Thallus: crustose, thin, continuous, surface: pale ochre, cream-colored to pale gray, smooth, dull Apothecia: delicate, fissurine, slightly elevated from the thallus, lirellate lirellae: straight or curved, partly branched and sometimes clustered together, 0.5-1.5 x 0.2-0.3 mm margin: thalline one slightly raised from the thallus, dark brown along the slit, often the dark lateral exciple shining through the thin thalline cover, which easily flakes off disc: gray to pale brown, slit-like, hidden by the margins or rarely open exciple: rudimentary and not carbonized at the base, laterally consisting of a narrow brownish layer partly with bark cells integrated, excipular lips ±distinctly brown to carbonized, towering above the hymenium and converging to the center, with many Ca-oxalate crystals embedded in the triangle between the lateral exciple and the thallus epihymenium: not differentiated hymenium: hyaline, not inspersed, 90-100 µm tall paraphyses: c. 1.5 µm thick, with hyaline, little thickened, warty tips periphysoids: well developed, covering the inner part of the excipular lips, hyaline, tips warty subhymenium: hyaline, 5-10 µm thick asci: clavate, 70-80 x 15 µm 8-spored ascospores: hyaline, 4-locular, slightly halonate (only young, immature spores?), 16-20 x 7-9 µm, I+ blue-violet Pycnidia and conidia: not found Spot tests: cortex and medulla K-, C-, KC-, P- Secondary metabolites: none detected. Substrate and ecology: on bark World distribution: probably pantropical Sonoran distribution: not yet found but expected due to its occurrence in coastal, central California and farther south. Notes: Wirth and Hale (1963: 98) mention Graphis humilis together with G. durandi, G. grossula, G. lecanorina, G. schizogramma and G. stromatoides as species similar to Graphis platycarpella Müll. Arg. The types of G. schizogramma and G. stromatoides could not be examined for this paper, but all other species listed by Wirth & Hale (1963) as well as Graphis furfuraceae Leight. (the oldest name within this species group) and Graphis timidula Nyl. are very similar and probably conspecific. All species show warty (to spiny) paraphysis tips and periphysoids, many crystals in the lateral exciple and identical ascocarp features. Also the chemistry (lacking any secondary metabolites) is the same in all species. The only differences are the spore size and the º of carbonization of the lateral exciple and the excipular lips.