Flora of New Zealand Series

≡Lecanora (Placopsis) dennanensis Zahlbr., Denkschr. Akad. Wiss. Wien math.-naturwiss Kl. 104: 348 (1941).

Holotype: New Zealand. Wellington, Mount Dennan, Tararua Mountains, c. 120 m, on schistose rock, [ix.1933], E. Chamberlain No. 188 – W. Isotype – CHR 347947.

Description : Thallus rosette-forming, closely attached, (1–)2–5(–8) cm diam., without a prothallus. Lobes plane to shallowly convex, rounded to flabellate at margins. Marginal lobes 1–3(–4) mm wide, contiguous, separated by narrow cracks from margins to centre. Upper surface greenish to olivaceous when moist, pale grey-green to whitish when dry, glossy (reminiscent of polished ivory), often minutely punctate-depressed (×10 lens) especially at or towards margins, without isidia, maculae, pruina or soredia. Cephalodia infrequent (1–2 per thallus), central, large, 1–8(–20) mm diam., prominent, raised above thallus, plicate–radiate, deeply cracked from centre to margins with the central parts often ±eroded. Apothecia sessile, scattered from margins to centre, often not well-developed, margins thick, persistent, smooth, glossy, concolorous with thallus, 0.2–2(–3) mm diam., disc dark-brown to brown-black, rather roughened to radially fissured, epruinose. Hymenium to 200 μm tall. Ascospores ellipsoidal, 15–18 × 6–8 μm.

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

N: Wellington (Kaimanawa Mts, Tararua Ra.). S: Nelson (Denniston Plateau, Mt Arthur), Westland (Kelly's Creek, Otira Gorge), Canterbury (Temple Basin, Arthur's Pass), Otago (Swampy Hill). On hard basalt and greywacke rocks, associating with other species of Placopsis, including P. fuscidula, P. lateritioides, P. perrugosa and species of Stereocaulon.

Endemic

Illustrations : Allan (1949: 21, fig. 42 – as Lecanora dennanensis); Murray (1963c: 101, pl. 5, fig. 44 – as Placopsis parellina; 1964: 30, pl. 5, fig. 44 – as Placopsis parellina).

Placopsis dennanensis is characterised by: a rosette-forming, tightly adnate thallus with plane to very shallowly convex, rounded to flabellate marginal lobes 1–3(–4) mm wide, contiguous, separated by narrow cracks from margins to centre. The thallus surface is glossy (reminiscent of polished ivory), often minutely punctate-depressed (×10 lens) especially at or towards margins. Cephalodia are infrequent (1–2 per thallus), central, large (to 20 mm diam), prominent, raised above thallus, plicate–radiate, deeply cracked from centre to margins with the central parts often ±eroded. It lacks isidia, maculae, pruina, or soredia. Apothecia are sessile, scattered from margins to centre, often not well-developed, margins thick, persistent, smooth, glossy, concolorous with thallus, 0.2–2(–3) mm diam., disc dark-brown to brown-black, rather roughened to radially fissured. Hymenium to 200 μm tall. Ascospores ellipsoidal, 15–18 × 6–8 μm.