Flora of New Zealand Series

Thallus orbicular, stellate-radiating, thalli often confluent, to 5 cm diam., closely attached, saxicolous. Lobes very narrow, to 3 mm wide, short, margins crenate, coralloid-sorediate, subascendent or downrolled, often passing into a coarsely wrinkled, warty crust. Soredia granular, grey-white or blackened, on lower surface of lobe apices. Upper surface roughened, wrinkled, ashy grey-white or grey-maculate in parts. Lower surface pale brownish, whitish in parts, rhizinate. Rhizines sparse, brown to black, short. Apothecia small, 1-3 mm diam., sessile, disc concave to plane, black ± grey-pruinose, exciple moderately thick, concolorous with thallus, irregular, waxy. Ascospores oblong-ellipsoid, 12-20 × 5-7.5 µm. Pycnidia rare. Chemistry: Cortex and medulla K+ yellow. Atranorin.

S: Canterbury (Hurunui River), Otago (Arrowtown). On rocks in dry, inland, eastern localities. Still very poorly collected.

Cosmopolitan

P. callosa is a small, closely attached, rosette-forming species characterised by the sorediate lower surface of the lobe apices. It associates with Lecanora dispersa, Physcia caesia and Teloschistes velifer. Because of its small size it is frequently overlooked.