Flora of New Zealand Series

Description : Thallus rosette-forming to irregularly spreading, very closely attached, 2–5(–8) cm diam., 50–150(–250) μm thick, tartareous; margins entire to shallowly notched or flabellate, flat to subconvex, without a marginal prothallus. Lobes 0.5–1.5(–2) mm wide at margins, soon confluent and continuous, separated by deep, gaping cracks and becoming conspicuously areolate, especially centrally. Areolae angular to irregular, 0.5–3(–4.5) mm diam, separated by deep cracks 0.2–1.0 mm wide and appearing as distinctive "islands" (×10 lens). Upper surface greenish when moist, pale greenish white to pinkish when dry, distinctively minutely cerebriform (×10 lens), without isidia, maculae, pustules, pruina or soredia. Cephalodia developing at margins of areolae, and soon spreading over surface of areolae, round to irregularly rosette-forming, 1–5(–8) mm diam., smoothly rounded at first, soon becoming plicate-cracked, the lobes of cephalodia separated by narrow to widely and deeply gaping cracks, purple-blue when wet, pale-pinkish when dry. Apothecia scattered, rather rare, somewhat immersed to ±sessile, (0.1–)0.5–1.0(–1.2) mm diam., solitary or 4 or 5 together, rounded to contorted through mutual pressure. Thalline margin swollen, prominent, 0.1–0.2 mm thick, glossy, smooth to subcrenulate, concolorous with thallus. Disc pale to dark red-brown, plane to concave, epruinose. Hymenium colourless to pale rose-pink, 130–200 μm tall (225–255 μm in the holotype). Ascospores uniseriate in ascus, ellipsoidal, 17.5–21 × 9–10 μm (20–22.5 × 11–12.5 μm in the holotype). Pycnidia immersed in thalline warts, ostiole prominent, red-brown to black, punctiform to flat, to 0.1 mm diam. Conidia filiform, 18–21 × 0.5–1 μm.

Chemistry : Thallus K+ yellowish, C+ red; containing gyrophoric and stictic acids.

S: Westland (Otira Gorge, Waitahi Valley), Otago (Glendhu Bluff, Teviot Valley), Southland (George Sound, Supper Cove Dusky Sound). C: (Mt Dumas, Perseverance Harbour). On moist, steeply sloping, riverside rocks. Known also from southern Chile (Galloway 2002d: 87).

Austral

Illustration : Lamb (1947: pl. XV, fig. 47).

Placopsis dusenii is characterised by: a thick, tartareous, closely attached, smooth, greenish white to pinkish, distinctively areolate thallus without a marginal prothallus; angular to irregular areolae, 0.5–3(–4.5) mm diam, separated by deep cracks 0.2–1.0 mm wide and appearing as distictive "islands" (×10 lens), the surface appearing characteristically minutely cerebriform, and without isidia, maculae, pustules, pruina or soredia; cephalodia are attached to areolae or discrete, separated by deep cracks, pale-pinkish when dry, purplish when wet, level with thallus surface or spreading very slightly above the surface; apothecia scattered, rather rare, somewhat immersed to ±sessile, (0.1–)0.5–1.0(–1.2) mm diam., solitary or 4 or 5 together, rounded to contorted through mutual pressure, margins swollen, prominent, 0.1–0.2 mm thick, glossy, smooth to subcrenulate, concolorous with thallus; the disc is pale to dark red-brown, plane to concave, epruinose; ascospores uniseriate in ascus, ellipsoidal, 17.5–21 × 9–10 μm; pycnidia immersed in thalline warts, ostiole prominent, red-brown to black, punctiform to flat, to 0.1 mm diam.; conidia filiform, 18–21 × 0.5–1 μm.