Alyxoria sierramadrensis

The thallus of Alyxoria sierramadrensis forms patches about 1–3 cm (0.39–1.18 in) across, composed of convex, elongate lobes or areoles whose pale brown surface is usually masked by a dense white pruina. In section it shows a well-developed upper cortex, a layer of orange-stained medulla containing anthraquinones, and a dark, loosely hyphal lower surface, with a trentepohlioid green alga as photobiont. The black ascomata (fruiting bodies) are scattered, rounded to shortly elongated, with a slightly raised margin surrounding a flat, widely exposed disc that is thickly covered in white pruina. Ascospores are hyaline, narrowly oblong to somewhat club-shaped, three-septate, typically 19–23 μm long and 7–9 μm wide, and surrounded by a distinct gelatinous sheath. Chemical tests and thin-layer chromatography reveal several unidentified anthraquinones and UV-fluorescent compounds, and together with the distinctive ascomata and spores these features separate the species from superficially similar placodioid lichens in genera such as Placolecis and Roccellina.^[2]

The species grows on exposed limestone outcrops in semi-humid parts of the Sierra Madre Oriental, where it occurs on steep or vertical rock walls within xerophytic and Piedmont scrubland communities that include scattered oaks. It has been recorded from six localities in the Mexican states of Coahuila and Nuevo León, at elevations of roughly 800–1,500 m (2,600–4,900 ft), and often co-occurs with other calcicolous lichens such as Bagliettoa calciseda, Psora pseudorussellii, Squamulea galactophylla, and Xanthopsorella texana. Field observations indicate that Alyxoria sierramadrensis can be locally frequent in suitable habitats, but many populations fall within the rapidly expanding metropolitan area of Monterrey, where quarrying of limestone and poor air quality are ongoing concerns; the authors therefore suggest that similar habitats in neighboring Mexican states and in adjacent Texas should be surveyed to clarify its full range and conservation status.^[2]