Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: areolate to rimose-areolate or becoming sub-squamulose, overall up to 5 cm wide areoles: irregular in shape, round to angular, without a stipe, (0.3-)1-2 mm wide, up to 1 mm thick, dispersed or contiguous, often swelling with development of apothecia and becoming nearly verruculose; rim: sometimes upturned or lobate, sometimes detached, concolorous with surface upper surface: light or dirty yellow-brown to dark brown, dull, subconcave to flat, uneven, undulate, smooth to rough, usually epruinose upper and lateral cortices: paraplectenchymatous but intergrading into anticlinal prosoplectenchyma, 30-50 µm thick, cells: various, sometimes completely opaque; syncortex: c. 10 µm thick, with ±periclinal hyphae, same color as eucortex; eucortex: upper layer with thin dark brown layer and lower layer indistinct and yellowish brown algal layer: ±70µm thick, penetrated by hyphal bands, upper and lower surface uneven, algal cells up to 15 µm wide medulla: prosoplectenchymatous, white, with hyphal bands sometimes distinct and anticlinal, continuous with attaching hyphae lower surface: corticate and same color as upper surface, or colorless, dark, or pale attachment: broad, occasionally elevating areole (gomphate) but not forming a stipe Apothecia: 1-7 per areole or squamule, 0.1-0.9 mm across, round to uneven disc: reddish to dark brown and ±black, very rough, concave to level parathecium: 10-30 µm wide epihymenium: yellowish brown or darker, coherent, 10-20 µm thick hymenium: hyaline to yellowish brown, conglutinated, (110-)120-140(-200) µm tall; paraphyses: 1-1.5(-2) µm wide at base, septate with cells shorter in upper part, ±constricted, apices ±unexpanded subhymenium: hyaline to pale yellow, indistinct, 20-30 µm thick; hypothecium: 10-20 µm thick asci: cylindrical to subclavate, 100-110 x 10-30 µm, 100+-spored ascospores: hyaline, simple, ellipsoid, 3-4 x 1-1.5 µm Pycnidia: not seen Spot tests: UV-, all spot tests negative Secondary metabolites: none detected. Substrate and ecology: on sandstone or crumbling granite in California World Distribution: North America (California and Utah) Sonoran distribution: southern California. Notes: The thallus is considered as chasmolithic in the key because it grows in upper disintegrating layer of its substrate. Although some old contiguous specimens can appear epilithic, they generally have abundant mineral particles lodged between the areoles. Magnusson considered Acarospora hassei Herre to be a synonym of A. smaragdula var. lesdainii (1929b). The author originally accepted this synonymy (2004). But specimens seen during this study from Europe of var. lesdainii were definitely A. smaragdula s. str. and the variety or subspecies classification looked like it should be dropped. In contrast to other Acarospora groups, this author thinks Magnusson was a "lumper" in the smaragdula complex, and treated unrelated species as varieties based on plesiomorphic character states of the algal layer, paraphyses and ascospores. The author considers thallus characters as synapomorphic, reflecting the morphological expression of the genetic divergence of related species. The different species concepts of the smaragdula group still have to be tested with molecular studies. At this time, molecular studies would be rather useless if specimens are not carefully distinguished because herbaria annotations in North America and Europe show no general agreement in taxonomic concepts. It should be noted that this author also thinks var. murina (Sand.) H. Magn. is a separate species based on thallus characters but has only seen one authentic specimen that was not the type.