Flora of New Zealand Series

Holotype: New Zealand. South I., Nelson, Larrikins Creek, Mokihinui River, 41º36.4's, 172º16.5'E, 360 m, on limestone rocks and bedrock of creek bed, through Nothofagus fusca forest, 18.iv.1995, D. Glenny 5939 – WELT L 4815.

Description : Thallus closely attached, lobate, orbicular at first, growing at margins and dying centrally, forming distinctive concentric circles or arcs to 50 cm diam., individual bands of thallus 1–4(–7) cm wide, margins entire to delicately notched or incised, flabellate, flat to subconvex, without a marginal prothallus. Lobes contiguous, parallel, radiating from near centre to periphery, or complexly interlocking, convex, 1–2 mm wide and to 2 cm long, broadening to 3–4 mm at periphery, separated by narrow cracks. Upper surface pale olive-greenish when moist, grey-brown to olive-brown when dry, densely to lightly white-pruinose, pruina farinose to crystalline, commonly developed in spots near margins reminiscent of maculae, smooth to shallowly wrinkled, becoming areolate and epruinose centrally, without isidia, pseudocyphellae or soredia. Medulla white, visible at dying edge of eroding thalline bands. Photobiont green, chlorococcoid, 8–10 μm diam. Cephalodia developing in concentric lines or bands near centre, absent from margins, orbicular, 1–3(–5) mm diam., hemispherical and smooth at first, becoming plicate–ridged and with deep radiating cracks at maturity, grey-blue when moist, pale pinkish brown when dry, with or without a thin, white, glistening pruina; cyanobiont Scytonema, in chains, cells compressed, cylindrical to fabiform, 8–10–12.5 μm diam. Apothecia scattered centrally among cephalodia, sessile, constricted at base, solitary, round, 0.5–1.0 mm diam., disc concave to plane, pale red-brown, thickly white-pruinose, obscured by margins. Thalline margin, persistent, smooth, swollen, concolorous with thallus, white-pruinose and contrasting with disc. Proper margin thin, concolorous with disc, slightly raised above level of disc, often somewhat glossy and contrasting with white-pruinose thalline margin. Epithecium pale-brownish, 20–30(–37.5) μm thick. Hymenium 180–250 μm tall, colourless; paraphyses slender, septate, unbranched, to 2.5 μm diam., apices not swollen. Hypothecium dilute yellow-brown or orange-brown, densely interwoven, 75–100(–125) μm thick. Asci cylindrical, 175–250 × 25–27.7 μm, wall at apex 5–7 μm thick, at sides 1.5–2.5 μm thick. Ascospores uniseriate, ovoid to broadly ellipsoidal, apices rounded or with one end pointed, comprising a large vacuole with clear, pale yellowish pink contents surrounded by granular-oily ascoplasm, 25–27(–28.5) × 13–15 μm; wall smooth, 1–1.5 μm thick. Pycnidia widely scattered on surface of lobes, immersed, to 200–250 μm diam.; ostiole punctate-depressed, red-brown. Conidia filiform, curved, 16.5–20 × 0.5 μm.

Chemistry : Thallus K−, C+ red. KC+ red, Pd−; containing gyrophoric acid (major), lecanoric acid (minor) and methyl lecanorate (minor).

S: Nelson (Thousand Acre Plateau, Matiri Ra., Mokihinui River), Westland (Waitaha River headwaters). On smooth greywacke, limestone and calcareous mudstone, in subalpine to high-alpine sites of high rainfall W of the Main Divide. Still very poorly collected.

Endemic

Illustration : Galloway (2004a: 155, fig. 3).

Placopsis centrifuga is characterised by: eroding bands of thallus 1–4(–7) cm wide, forming single to multiple concentric rings or arcs (up to 50 cm diam., the area within each ring dying and being replaced by new, smaller rings), closely attached to smooth rock, extending at margins and dying centrally; whitish pruina in patches or generally over upper surface; orbicular cephalodia developing in concentric lines or bands towards centre; small, sessile apothecia, 0.5–1 mm diam., scattered among cephalodia; hymenium 180–250 μm tall; ascospores broadly ellipsoidal to oval, 25–27(–28.5) × 13–15 μm. It differs from P. fuscidula (q.v.) in the nature of the thallus (P. fuscidula never forms concentric rings of thallus), in the rather denser marginal, maculate pruina, and the larger spores [those of P. fuscidula are 17.5–22.5 × 9–12.5 μm]. These characters also distinguish it from P. pruinosa.