Flora of New Zealand Series

Holotype: New Zealand. Otago, Boyd's Bush [North Taieri] near Dunedin, on schist rock, 7.vii.1933, J.S. ThomsonT497 [ZA 74] – W. Isotypes – CHR 163000, OTA 029818.

Description : Flora (1985: 477).

Chemistry : TLC−, all reactions negative.

S: Nelson (Brook Stream), Marlborough (above Ship Cove), Canterbury (Dyer's Pass, Banks Peninsula), Otago (Trotter's Gorge, Mt Watkin, Silver Peaks, Hammond's Hill Merton, Boyd's Bush N Taieri, Dunedin, Goat I. Otago Harbour, Akatore, Tautuku Bay), Southland (Doubtful Sound, Supper Cove Dusky Sound). St: (Noble I., Port Pegasus). A: On coastal rocks above Verrucaria zone, and on rocks in damp, humid sites in coastal and lowland forest, s.l. to 400 m. It associates with Dirina neozelandica, Opegrapha diaphoriza, Pertusaria graphica, Placopsis cribellans, and Tylothallia pahiensis on exposed rocky shore habitats, while in humid, shaded sites, it associates with species of Leptogium, Pannaria leproloma, P. microphyllizans and Psoromidium aleuroides.

Endemic

Illustrations : Malcolm & Galloway (1997: 139); Malcolm & Malcolm (2001: 68).

Psoroma melanizum is characterised by: the saxicolous habit; the squamulose thallus, closely attached in compact rosettes and often mosaic-forming, 1–3 cm diam., bordered by a thin, black, byssoid prothallus, 1–2 mm wide; the thalline squamules are minute, 0.2–1.0 mm diam., yellowish brown to pale or whitish at margins, often secondarily lobulate and dispersed at margins, coalescent centrally forming a diffract-areolate crust; the scattered cephalodia, marginal on squamules, wrinkled-plicate; the frequent, sessile, predominantly central apothecia, 0.5–1.5 mm diam., the disc brown-black, plane to subconcave, with thin, crenulate margins concolorous with thallus; and subglobose to globose ascospores, 10–15(–16.5) μm diam., with oily-granular contents and a perispore 1–3 μm thick.