Flora of New Zealand Series

=Rhizocarpon obscuratum, auct. non (Ach.) A.Massal.

=Rhizocarpon convexulum Zahlbr., Denkschr. Akad. Wiss. Wien math.-naturwiss. Kl. 104: 321 (1941).

=Rhizocarpon thomsonii Zahlbr., Denkschr. Akad. Wiss. Wien math.-naturwiss. Kl. 104: 322 (1941).

=Rhizocarpon thomsonii f. fuscidulum Zahlbr., Denkschr. Akad. Wiss. Wien math.-naturwiss Kl. 104: 321 (1941).

Rhizocarpon convexulum. Holotype. New Zealand. Wellington, Manawatu Gorge, rock surface in road-cutting, E. Chamberlain W62 – W. Isotype – CHR 347983.

Rhizocarpon thomsonii. Holotype: New Zealand. Otago, Mac's Valley near Dunedin, on rock, J.S.Thomson ZA 15 – W. Isotypes – not seen.

Rhizocarpon thomsonii f. fuscidulum : Holotype: New Zealand. Otago, Waikouaiti Reservoir, on schistose rock, J.S. Thomson T1580 [ZA 21] – W. Isotypes CHR 347985, OTA 029385.

Description : Thallus effuse or tartareous in discrete patches, 1–2 cm diam., coalescing to cover larger areas (8–10 cm diam.), grey or greyish white to brown, areolate, thin to moderately thick, rarely subsquamulose or nodulose, with a prominent marginal black prothallus, prominent in shaded sites. Areolae 0.2–0.4(–1) mm diam., separated by very narrow, black cracks, plane to subconvex, smooth, matt. Apothecia black, lecideine, innate to sessile, scattered among areolae, disc plane to subconvex, epruinose, (0.2–)0.4–0.8(–1) mm diam. Epithecium olivaceous, or rarely brown (K+ green-blue, N+ red). Paraphyses slender, c. 1 μm thick, not much swollen or pigmented at apices. Hypothecium thick, dark-brown. Asci cylindrical to clavate, 65–80 × 25–35 μm, 8-spored. Ascospores colourless, halonate, submuriform (3–)5–10(–14) cells in optical section, 25–27(–30) × 11–12(–13.5) μm. Pycnidia not seen.

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

N: Wellington (Manawatu Gorge, N of Castlepoint). S: Canterbury (Banks Peninsula, Herbert Peak), Otago (Teviot Road, Waikouaiti Reservoir, Mac's Valley, Coutt's Gully Taieri Beach), Southland (Dean Burn, Waikaia River). C: On coastal and inland siliceous rocks in tussock grassland, generally at lower altitudes. Associating with Acarospora spp., Rhizocarpon geographicum, Xanthoparmelia mougeotina. It is a colonising species, occurring early in the succession on freshly exposed, rock surfaces (Fryday 2000b). Known also from Great Britain, Europe, the high Arctic, Morocco, Tunisia, Turkey, the Ukraine, Asia, China, South Africa, North America, Venezuela, Bolivia, Chile, Argentina, Falkland Is, Antarctica, and Australia (Lynge 1932, 1936; Feuerer 1978, 1991; Purvis et al. 1992; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Wirth 1995b; Egea 1996; John 1996; Kondratyuk et al. 1996a; Seaward 1996; Elvebakk & Hertel 1997; Galloway & Quilhot 1999; Diederich & Sérusiaux 2000; Scholz 2000; Fryday 2000b; Brodo et al. 2001; Hafellner & Türk 2001; Llimona & Hladun 2001; Øvstedal & Lewis Smith 2001; Coppins 2002b; McCarthy 2003c, 2006; Nimis & Martellos 2003; Ihlen 2004a; Santesson et al. 2004).

Bipolar

Illustrations : Dobson (1992: 298 – as Rhizocarpon obscuratum; 2000: 343; 2005: 389); Wirth (1995b: 805D); Fryday (2000b: 212, fig. 1C); Brodo et al. (2001: 638, pl. 778); Ihlen (2004a: 540, fig. 8E; 556, fig. 29).

Rhizocarpon reductum is characterised by: the brown to pale-grey or greyish white, moderately thick, areolate thallus; the small (25–30 × 11–13.5 μm), hyaline, submuriform to muriform ascospores; and the occurrence of stictic acid. It is discussed in detail by Fryday (2000b: 210–214) and Ihlen & Fryday (2002). Ihlen (2004a) includes specimens with smaller ascospores with fewer septa, and which also have a smooth apothecial disc, in R. postumum (q.v.).