Flora of New Zealand Series

Description : Thallus areolate, in patches to 3 cm diam., on a black prothallus. Areolae minute, 0.2–0.3 mm diam., rounded to angular, crowded or dispersed, flat to convex, whitish, grey-white, grey-brown to dark-brown. Medulla I+ blue. Apothecia small, 0.5–1 mm diam., black, between areolae, flat, matt, slightly roughened, sometimes pruinose, margin persistent or disappearing, concolorous with disc. Hymenium to 100 μm tall, colourless to brownish; epithecium dark violet-brown, K+ violet-red. Hypothecium dark violet-brown to dark olive-brown. Asci clavate (4–6)8-spored. Ascospores submuriform colourless to slightly darkening, transversely 1–5-septate, central 1–2 cells with longitudinal walls, 24–32 × 11– 15 μm.

Chemistry : Thallus K+ yellow, C−, KC−, Pd−; containing stictic acid.

S: Canterbury (Herbert Peak Banks Peninsula), Otago (Abbott's Hill, Maungatua), Southland (Tiwai Point). St: (Cooks Arm Port Pegasus). On sunny rock outcrops in tussock grassland with Acarospora sp., Candelariella vitellina, Immersaria athroocarpa, Lecanora farinacea, Placopsis perrugosa, Rhizocarpon eupetraeum, R. geographicum, R. grande and Xanthoparmelia mougeotina, on coastal quartz pebbles at Tiwai Point, and on maritime rocks in southern Stewart I. Known also from Great Britain, northern Europe, Scandinavia, Svalbard, Greenland, Morocco, the Balkans, Greece, Turkey, the Ukraine, North America, Chile, Australia and Antarctica (Lynge 1932, 1936; Thomson 1969; Feuerer 1978, 1991; Purvis et al. 1992; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Wirth 1995a, 1995b; Egea 1996; John 1996; Kondratyuk et al. 1996a; Elvebakk & Hertel 1997; Galloway & Quilhot 1999; Diederich & Sérusiaux 2000; Scholz 2000; Hafellner & Türk 2001; Llimona & Hladun 2001; Øvstedal & Lewis Smith 2001; Coppins 2002b; McCarthy 2003c, 2006; Nimis & Martellos 2003; Feuerer & Timdal 2004; Ihlen 2004a; Santesson et al. 2004).

Cosmopolitan

Illustrations : Feuerer (1978: 85); Wirth (1987: 413; 1995a: 535, pl. 55J; 1995b: 803, 805J); Foucard (1990: 241, pl. 275); Ihlen (2004a: 540, fig. 7A; 548, fig. 17).

Rhizocarpon distinctum is characterised by: a grey-brown to dark-brown areolate thallus on a black prothallus; minute (0.2–0.3 mm diam.), rounded to angular, flat to convex areolae; an amyloid (I+blue) medulla; scattered black apothecia, the disc slightly roughened to pruinose; the dark violet-brown epithecium (K+ violet-red); (4–6)–8-spored asci; and colourless, submuriform ascospores, 24–32 × 11–15 μm, and stictic acid in the medulla.