Rhizocarpon grande (Flörke) Arnold
Lecidea petraea var. fuscoatra f. grandis Flörke in Flotow, Flora 11: 690 (1828).
Thallus crustose, areolate, spreading or ± orbicular to 5 cm diam., with a prominent black marginal prothallus. Areolae 0.6-0.9(-1.6) mm diam., ± dispersed, convex, often constricted, the areolae then glebulose, smooth, ashy brown, sometimes greyish-whitish or tinged violet, without pruina or soredia. Apothecia black 0.5-0.8(-14) mm diam., between areolae, angular to rounded, disc flat, black, dull sometimes becoming convex, margins thin, entire or disappearing. Ascospores 8 per ascus, muriform, many-celled, dark brown, halonate, 24-46 × 11-16 µm. Chemistry: Medulla K- or ± yellow, C+ red, Pd-. Gyrophoric and ± stictic acid.
S: Canterbury, Otago. On alpine rocks. Still very much undercollected.
Cosmopolitan
