Physcia nubila
Description : Thallus rosette-forming to irregularly spreading, 1–3(–4) cm diam., closely attached from margins to centre. Lobes variable, thin to thick, (0.5–)1–2(–3) mm wide, 5–10(–20) mm long, convex, flabellate, imbricate from margins to centre, branching irregular. Margins delicately scalloped, notched or incised, to minutely lobulate, apices slightly curled under, thickened (×10 lens), erose-sorediate towards inner parts. Upper surface white, creamish to grey-white, sometimes suffused grey-black at apices, areolate–scabrid (×10 lens) at apices, matt or minutely roughened–fibrous (×10 lens) elsewhere, sometimes white-pruinose at or close to margins. Soralia marginal, towards inner parts of lobes, erumpent-erose, sometimes coalescing and forming extensive sorediate patches centrally; soredia coarsely granular, white or grey-white. Lower surface corticate, creamish white to pale-buff, with a narrow, darker, marginal zone, smooth, rhizinate. Rhizines scattered, rather sparse at margins, more numerous centrally, concolorous with lower surface, simple, with an apical squarrose tuft, 0.5–0.8 mm long. Apothecia rare, generally absent (when present often abundantly developed), sessile, constricted at base, rounded, 0.5–1(–1.5) mm diam., thalline exciple persistent, thick, swollen, entire to ±scalloped, concolorous with thallus, not becoming sorediate in older fruits; disc concave to plane, matt, dark-brownish to black, epruinose. Epithecium chestnut-brown, 15–18 μm thick. Hymenium colourless, 65–85(–90) μm tall. Hypothecium colourless, opaque, intricately interwoven. Ascospores grey-brown, Pachysporaria -type, broadly ellipsoidal apices, obtuse, (16.5–)20–23 × 8–10.5 μm. Pycnidia occasional to common, laminal, immersed, black, punctiform, minute (×10 lens).
Chemistry : Cortex K+ yellow; medulla K+ yellow; containing atranorin and zeorin.
N: Northland (Kerikeri Inlet, Great Barrier I.), Auckland (Rangitoto), South Auckland (Waikawau, Hot Water Beach, Coromandel Peninsula), Taranaki (N of Mapiu), Wellington (Kapiti I., Wellington) S: Nelson (Kaihoka), Marlborough (Queen Charlotte Sound), Westland (Ship Creek N of Haast), Otago (Shag Point to Nugget Point), Southland (Dusky Sound, Pahia Point). St: (Halfmoon Bay, Paterson Inlet, Port Pegasus). Ch: (SW of Waitangi). Sn: On coastal rocks close to high tide mark. Known also from East and South Africa, South America and Australia (Moberg 1990, 2001, 2004b; McCarthy 2003c, 2006).
Palaeotropical
Illustrations : Moberg (1990: 335, fig. 12).
Physcia nubila is characterised by: the saxicolous (coastal rocks) habit; the marginal (also laminal towards centre of thallus), often prominent soralia that are either confined to the lobe sinuses or develop along the whole lobe margin. It differs from P. undulata, which has more irregular lobes (undulating), a thinner thallus, and a chemistry with different triterpenoids (Moberg 2001: 302).
