Aspicilia prestensis

Aspicilia prestensis is a crustose lichen with a thallus that is whitish to ash-grey and divided into angular patches (areoles). The thallus is typically 2–7 cm across and about 0.2–0.5 mm thick; the areoles are roughly 0.3–2.4 mm wide, with outer areoles often larger and more subdivided than central ones. A dark marginal line (the hypothallus) may be visible in some specimens.^[2]

The apothecia (disc-like fruiting bodies) are small (about 0.2–0.7 mm across), black, and typically sit in the areoles, often several per areole; their discs are dull and finely roughened, without a powdery coating. Microscopically, the asci contain eight colourless spores that are ellipsoid to slightly elongate, about 17.5–24.5 × 9.5–14 μm. The asexual propagules (conidia) are thread-like and about 14.5–21 × 1 μm, straight to slightly curved. Chemical spot tests on the thallus are typically K+ (yellow turning blood-red) and P+ (yellow to yellow-orange), consistent with norstictic acid as the main lichen substance.^[2]

This is a rock-dwelling species that grows on exposed, non-calcareous (non-limestone) rocks, including gently sloping rock surfaces and boulders. It is reported from montane to alpine elevations, and tends to occur in open sites, often in full sun, though it can tolerate a range of light conditions.^[2]

It is known from the Pyrénées-Orientales, the Massif Central, and the Alps, where it appears to be fairly common; the authors also suggest it is likely to be widespread in Europe's non-calcareous high mountains. Because it has frequently been confused with A. cinerea and A. epiglypta, older records under those names may need re-checking in mountainous regions.^[2]