Cora casasolana

The thallus of Cora casasolana is terricolous and foliose, forming rosettes up to 10 cm across among herbaceous vegetation. It consists of three to seven semicircular lobes, 1–3 cm wide and 1–2 cm long, that ascend slightly and branch sparingly without radial sutures. Fresh lobes are dark olive-green to olive-grey, lacking concentric color rings; the thin, rolled-in (involute) margins are light yellowish-grey, becoming white-grey in the herbarium. The upper surface is even to very shallowly undulate (wavy) when hydrated and becomes undulate-rugose on drying, remaining glabrous throughout. The lower surface lacks a cortex (ecorticate) and exposes a whitish, felty-arachnoid medulla.^[2]

In cross-section the thallus is 200–300 micrometres (μm) thick. A viaduct-shaped upper cortex, 20–30 μm deep, overlies a 50–70 μm zone of anticlinal hyphae. The photobiont layer is 100–150 μm thick (orange above, aeruginous-green below); the medulla is 30–60 μm and bears numerous short, partly branched, papilliform hyphae 3–4 μm wide. Clamp connections are absent. No hymenophore has been observed, and thin-layer chromatography revealed no secondary metabolites.^[2]

Cora casasolana differs from the epiphytic relatives C. totonacorum and C. haledana by its terrestrial habit; all three share medium-sized olive-to-dark-green lobes and papilliform hyphal appendages on the lower medulla. Within the Mexican fungus it grows sympatrically with C. ixtlanensis but is readily distinguished by its olive-green lobes and conspicuous medullary papillae.^[3]

Cora casasolana is so far known only from its type locality at 2,990 m (9,810 ft) elevation on Cerro Pelón, Sierra Juárez de Oaxaca, southern Mexico. It grows on soil among grasses and low shrubs in a mosaic of cloud forest edge and alpine-like shrubby grassland, environments characterized by frequent fog, high humidity and intense ultraviolet radiation.^[2] Cerro Pelón is the richest documented Mexican site for Cora, harbouring six species and one subspecies.^[3]