Porpidia speirea
≡Lichen speireus Ach., Lichenogr. suec. prodr.: 59 (1799) ["1798"].
Description : Thallus forming prominent rounded to spreading white colonies, 1–5 cm diam., with a well-developed to indistinct, black prothallus. Upper surface areolate, minutely granular–roughened, chalky, white to creamish to pale-greenish grey. Medulla I+ violet. Apothecia frequent, 0.2–1.2(–2) mm diam., often clustered centrally to scattered, usually remaining subimmersed often surrounded by a break in the thallus or with a distinct, thalline collar, disc black, concave to convex, patchily white-pruinose at first, epruinose at maturity and then sometimes with central plugs of sterile tissue. Epithecium greenish brown. Hymenium colourless, 75–90 μm tall. Excipular hyphae 3–5 μm diam. Ascospores 12–19 × 6–7 μm.
Chemistry : Thallus K−, C−, KC−, Pd−; containing confluentic, 2'- O -methylmicrophyllinic, and 2'- O -methylperlatolic acids.
S: Marlborough (Kaikoura), Canterbury (Weka Pass). On limestone. Known also from Great Britain, Europe, Scandinavia, North America, Asia and Australia (Inoue 1982; Gowan 1989b; Galloway & Coppins 1992; Gowan & Ahti 1993; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Scholz 2000; McCarthy 2003c, 2006; Nimis & Martellos 2003; Fryday 2005).
Cosmopolitan
Illustrations : Inoue (1982: 44, fig. 23C; pl. IV, figs 3, 4 – as Lecidea speirea); Gowan (1989b: 52, fig. 55); Foucard (1990: pl. 265); Dobson (2000: 321; 2005: 362).
Porpidia speirea is characterised by: the saxicolous habit (basicolous rocks); the chalky, roughened, white to creamish or pale-greenish grey thallus; subimmersed, black apothecia, 0.2–1.2(–2) mm diam.; ascospores, 12–19 × 6–7 μm; and confluentic acid as major secondary metabolite.
