Rhizocarpon disporum
≡Lecidea dispora Nägeli ex Hepp, Flecht. Eur.: No. 28 (1853).
Description : Thallus bullate-areolate, grey to grey-brown, spreading in patches on a black prothallus 1–2 cm diam. Areolae constricted at base, convex, smooth. Medulla I−. Apothecia black, epruinose to 0.8 mm diam., convex with a thin margin at first, disappearing with age. Hymenium colourless, 100–140 μm tall; epithecium red-brown, K+ violet-red. Hypothecium dark reddish brown to dark-brown. Asci 1-spored. Ascospores muriform with numerous cells, green-brown to dark-brown, 50–75 × 20–30 μm.
Chemistry : Thallus K+ yellow, C−, KC−, Pd−, I−; containing stictic acid (Hertel (1985b: 314).
S: Otago (Roxburgh). On schist outcrops on a steep, dry sunny slope in grassland (Hertel 1985b: 314). Known also from Europe, Scandinavia, Greenland, Morocco, Turkey, the Ukraine, North America, Bolivia, Chile, Australia, South Orkney Is, South Shetland Is and Antarctica (Lynge 1932, 1936; Thomson 1968a, 1979; Feuerer 1978, 1991; Buschardt 1979; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Wirth 1995a, 1995b; Egea 1996; Kondratyuk et al. 1996a; Galloway & Quilhot 1999; St Clair 1999; Diederich & Sérusiaux 2000; Scholz 2000; Brodo et al. 2001; Llimona & Hladun 2001; Hafellner & Türk 2001; Øvstedal & Lewis Smith 2001; McCarthy 2003c, 2006; Nimis & Martellos 2003; Feuerer & Timdal 2004; Santesson et al. 2004; Søchting et al. 2004).
Bipolar
Illustrations : Feuerer (1978: 84); Wirth (1995a: 535, pl. 55H; 1995b: 805H); St. Clair (1999: 177); Brodo et al. (2001: 635, pl. 773).
Rhizocarpon disporum is characterised by: the bullate-areolate thallus, the areolae grey to grey-brown, on a black prothallus; 1-spored asci; muriform ascospores, 50–75 × 20–30 μm; and stictic acid in the medulla. Rhizocarpon disporum is very closely related to R. geminatum, which differs only in having 2-spored asci. However, some collections have both 1- and 2-spored asci in the same apothecium, and more work is required to clarify the separation of these two taxa.
