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Data Set Maintenance: Data set standard item. Data set author(s): Rambold G. Data set reviewer(s): Elix J. A. (95-06-01) and Scholz P. (02-05-15); revised; to be published after submission.

Nomenclature: Current taxonomic status: accepted. Taxonomic rank: genus. Number of known taxa within this rank: 19. Myelochroa. Parmeliaceae Zenker (1827); Lecanorineae; Lecanorales.

Taxonomic Literature: Elix J.A., Bryologist 96: 359-383 (1993); Elix J.A. & Hale M.E.,

Mycotaxon 29: 233-244 (1987); Hale M.E., Smithsonian Contr. Bot.
33:
1-60 (1976); Nash T.H. & Elix J.A. in: Nash T.H. III et al.
(eds) Lichen Flora of the Greater Sonoran Desert Region vol. 1, 288-
289, Tempe (2002).

Biogeography: Checklist records: Sonoran Desert, Thailand, United States and Canada (continental), and Republic of South Africa.

Lichen Photobionts: Primary photobiont present; chlorococcal. Primary photobiont taxonomy: Trebouxia; Trebouxiaceae; Trebouxiales, Trebouxiophyceae, Eukariota. Secondary photobiont absent.

Thallus: Foliose, not subdivided parts, lobed. Thallus Outline: Soon disappearing. Upper Surface: Grey; special structures absent or present:; not pseudocyphellate; ciliate; without hairs; not isidate or isidiate; not sorediate; not cephalodiate; not lobulate; without granules granules, without thalloconidia thalloconidia. Lower Surface: Attached by holdfasts; special structures present:; not pseudocyphellate; not cyphellate; rhizinate; without thalloconidia thalloconidia; not cavernulate; not tomentose.

Reproduction Strategy: Only known as sterile, asexually reproducing form or with sexual (and possible asexual) stages. Ascocarps: Apothecioid, orbicular, forming all across the thallus surface, soon sessile to substipitate. Margin: Prominent; external filaments absent. Exciple: Grey or white. Periphyses: Absent. Epithecium: Apical cells brown or brownish yellow. Interascal Hyphae: Present, scarcely branched, not or scarcely anastomosed. Hypothecium: White.

Asci: Tholus thickened, amyloid, with non-amyloid wide axial body and divergent amyloid flanks towards apex; dehiscence lecanoralean.

Ascospores: c. 8 per ascus, broadly ellipsoid or ellipsoid, 8-15 µm long, 5-10 µm wide, obtuse; septa absent; wall thin, not thickened at the septum, hyaline, in Lugol's Solution negative, wall not ornamented.

Conidiomata: Absent resp. not observed or present; pycnidial; immersed, formed all accross the thallus surface.

Secondary Metabolites: Present, of the following substance class(es): ß-orcinol depsides, ß-orcinol depsidones, (tri-)terpenoids, and secalonic acids.

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