Psora crenata
≡Endocarpon crenatum Taylor, Lond. J. Bot. 6: 156 (1847).
Description : Thallus squamulose, spreading, terricolous. Squamules up to 10 mm diam, isodiametric, rounded, adnate, scattered to contiguous, usually with a regular depression centrally. Upper surface bright-red to reddish brown, rarely ±brown, dull, pruinose in exposed parts near margins of squamules, or entirely white-pruinose, usually with some surface fissures. Margins concolorous with upper surface or white, usually downturned, entire to subcrenulate, underside pale-brown to white. Apothecia to 2 mm diam., marginal, plane, soon becoming strongly convex to hemispherical, immarginate, disc black, dull to shining, epruinose or rarely partly white-priunose. Asci clavate, 55–65 × 12–14 μm. Ascospores ellipsoidal, 12–16 × 6–8 μm. Pycnidia not seen.
Chemistry : Medulla K+ yellow, C−, KC−, Pd+ yellow; containing norstictic acid.
S: Otago (Fairfax Spur, Dunstan Mts). On schist soil in high-alpine zone – the dominant terricolous lichen in the habitat of the restricted endemic Myosotis albosericea. Known also from Europe, central Asia, North America including Mexico, South Africa, South West Africa and Australia (Schneider 1980; Timdal 1984b, 1986, 2002b; Filson 1996; Brodo et al. 2001; McCarthy 2003c, 2006).
Cosmopolitan
Illustrations : Weber (1962: pl. I, figs 5, 6 – as Lecidea decipiens); Schneider (1980: 95, fig. 12.6; 123, fig. 17.1; fig. 53); Timdal (1986: 260, fig. 8); Brodo et al. (2001: 599, pl. 723); Belnap et al. (2001a: 6, pl. 14).
Psora crenata is characterised by: the terricolous habit; broad, thick squamules (to 10 mm diam.), which usually have a regular central depression and downturned, ±entire margins; it always contains norstictic acid. Psora decipiens is similar, but its squamules are smaller (to 6 mm diam.), they lack a central depression and they have, especially when young, more upturned and more distinctly crenulate margins.
