Flora of New Zealand Series

Description : Thallus brown to grey-brown or dirty creamish grey, areolate, in irregular patches, 1–2 cm diam., the areolae close together or scattered on a black prothallus. Areolae peltate, plane to subconvex, round to angular, 0.2–0.5 mm diam., separated by narrow to deep cracks. Apothecia scattered to crowded, round to angular or deformed through mutual pressure, developed between areolae, 0.2–0.4(–0.5) mm diam., flat, matt, black, epruinose, with a thin, concolorous proper margin. Epithecium red-brown to dark purplish brown (K+ red), 8.5–15 μm thick. Hymenium colourless, 100–130 μm tall. Hypothecium densely interwoven, brown-black. Asci broadly clavate, 2-spored, 65–90(–112) × 25–30 μm. Ascospores muriform, colourless at first becoming greenish to olive-brown or dark-green at maturity, 40–50(–60) × 15–20(–23) μm.

Chemistry : Medulla Pd+ yellow or −, K+ yellow or K−; containing stictic acid and norstictic acid (±).

S: Canterbury (near Hanmer Springs, Waimakiriri riverbed), Otago (Canyon Creek Ahuriri Valley, Coronet Peak, W of Cromwell, Poolburn Reservoir, Teviot Valley), Southland (S Mavora Lake). On exposed rock outcrops in grassland, on rocks in grazed pasture, on damp, sloping rock surfaces in disused railway cutting, and on streamside rocks and lakeside rocks. Associating with Aspicilia cinerea, Buellia macularis, Lichina minutissima, Rhizocarpon geographicum, R. lecanorinum, R. submodestum, Verrucaria aquatilis, V. austroschisticola and Xanthoparmelia mougeotina. Known also from Great Britain, Europe, Scandinavia, Svalbard, Greenland, Greece, Turkey, the Ukraine, North America, Bolivia, South Shetland Is, and Antarctica (Feuerer 1978, 1991; Purvis et al. 1992; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Wirth 1995a, 1995b; John 1996; Kondratyuk et al. 1996a; Elvebakk & Hertel 1997; Diederich & Sérusiaux 2000; Scholz 2000; Hafellner & Türk 2001; Llimona & Hladun 2001; Øvstedal & Lewis Smith 2001; Coppins 2002b; Nimis & Martellos 2003; Feuerer & Timdal 2004; Santesson et al. 2004).

Bipolar

Illustrations : Feuerer (1978: 87); Moberg & Holmåsen (1982: 130); Wirth (1987: 413; 1995b: 810); Hansen (1995: 111).

Rhizocarpon geminatum is characterised by: the grey to grey-brown, areolate thallus; scattered, minute, black apothecia with a thin proper margin or becoming immarginate; a red-brown to purplish brown (K+ red) epithecium; 2-spored asci; and muriform, greenish to olive-brown to dark-green ascospores, 40–50(–60) × 15–20(–23) μm and stictic acid and ±norstictic acid in the medulla. Nomenclatural problems relating to earlier synonyms of R. disporum and their relevance to R. geminatum are discussed in Fryday (2002b: 454–456) and Fryday & Coppins (2003). The separation of R. geminatum from R. disporum, which differs only in having 1-spored asci, is discussed above under R. disporum.