Flora of New Zealand Series

Holotype: New Zealand. Westland, Fox River below glacier, 260 m, on scattered rocks and pebbles on vegetated rock slide above river, 10.viii.2003, D.J. Galloway 5613 – CHR 534103.

Description : Thallus orbicular, closely attached, (0.5–)1–3(–5) cm diam., in neat rosettes or forming more extensive, confluent patches, margins neatly plicate, entire to minutely notched, crenulate or lobulate, flat to subconvex, without a marginal prothallus. Lobes narrow, 0.2–0.5(–1.0) mm diam., convex, radiating from central parts to margins, closely contiguous from margins to near centre or separated by narrow to gaping cracks, 3–6 mm long, imbricate towards centre and there obscured by apothecia and cephalodia. Upper surface grey-green to olivaceous to lettuce-green when moist, greyish or pinkish fawn when dry, smooth, matt, epruinose, conspicuously white-maculate (×10 lens) when moist. Medulla white (C+ red). Photobiont green, chlorococcoid, cells rounded, thick-walled, 5–10 μm diam. Cephalodia large, central (occasionally smaller and submarginal), (1–2–)6–10(–12) mm diam., orbicular, wrinkled, radiate-plicate, epruinose, dark purplish blue when moist, pale-pink to salmon-pink when dry, spreading over thalline tissue, becoming deeply cracked with age, eventually eroding and separating into irregular "islands", or being overgrown by patches of new thalline tissue, apothecia and cephalodia; cyanobiont Scytonema in chains, cells compressed, rounded, ovoid to bean-shaped, (3–)5–10(–15) μm diam. Apothecia sessile, not much constricted at base, densely crowded, developed in characteristic concentric lines (2–8 rows) around central cephalodia, round to soon deformed through mutual pressure, (0.1–)0.2–0.8(–1.0) mm diam., disc shallowly concave to plane, pale to dark red-brown, matt, epruinose. Thalline margin entire, maculate (×10 lens), concolorous with thallus, most noticeable when dry, sometimes occluded by swollen disc when moist. Proper margin, persistent, entire, thin, slightly raised, paler than disc. Epithecium brownish, granular, 15–23 μm thick. Hymenium colourless, not inspersed with oil droplets, 135–155 μm tall. Hypothecium pale brown-pink to colourless, very densely interwoven, 110–135 μm thick. Asci cylindrical with a tapering foot, 130–150 × 11–15 μm, 8-spored. Ascospores uniseriate in ascus, broadly ellipsoidal to ovoid, apices rounded, contents oily-granular or vacuolate, 16.5–18.5 × 8–10 μm. Pycnidia occasional to frequent, towards lobe margins, immersed, to slightly swollen, 150–400 μm diam., ostiole, punctate-depressed brown-black to black, surrounded by a thin, maculate margin. Conidia filiform, straight or slightly curved, 15–40(–45) × 1–1.5 μm.

Chemistry : Thallus K−, C+ red, KC+ red, Pd−; containing gyrophoric acid.

S: Nelson (Mt Arthur), Westland (Fox Glacier, Karangerua River, Haast), Southland (Cascade Creek, Mararoa River, near Lake Monowai). It is a common lichen of riverside, riverbed, and rockslide boulders, stones and pebbles and on moraine detritus in high-rainfall areas W of the Main Divide, and on rocks and boulders in roadside cuttings in wetter areas E of the Main Divide. Commonly forming interlocking mosaics with other species of Placopsis, including P. brevilobata, P. clavifera, P. elixii, P. hertelii, P. illita, P. perrugosa, P. rhodophthalma and P. salazina; species of Porpidia, Stereocaulon colensoi and S. corticatulum.

Endemic

Illustrations : Galloway (2004c: 111, fig. 7).

Placopsis polycarpa is characterised by: the saxicolous habit; the neat, orbicular, rosette-forming thalli; narrow, convex lobes with conspicuous, marbled white maculae (×10 lens); and densely clustered, small apothecia (often in radiating rows) occupying most of the centre of the thallus.