Flora of New Zealand Series

≡Lichen decussatus Vill., Hist. pl. Dauph. 3: 964 (1789).

Description : Flora (1985: 591).

Chemistry : Gyrophoric (major), lecanoric and ovoic (minor) acids (Feige et al. 1987; Narui et al. 1996).

S: Marborough (Mt Tapae-o-uenuku), Westland (Mt Haast), Canterbury (Mt Hutt, Two Thumbs Ra., summit rocks Mt Cook, Mt Peel, Mt Nessing Hunters Hills), Otago (St Mary Ra., The Remarkables, Old Man Ra., Umbrella Mts, Garvie Mts, Dunstan Mts, Hawkdun Ra., Mt Ida, Mt Pisgah, Poolburn Reservoir, Rough Ridge, Rock & Pillar Ra.). On steeply sloping to ±vertical rock faces, often in very exposed, high-light environments (New Zealand's highest macrolichen!). Known also from the European Alps, Scandinavia, Svalbard, Greenland, Siberia, Asia, North America, Ecuador, Argentina, Chile, East Africa, Australia and maritime Antarctica (Frey 1933, 1936b; Llano 1950; Filson 1974b; Krog & Swinscow 1986, 1988; Sancho et al. 1992, 1999; Nimis 1993; Santesson 1993; Wei & Jiang 1993; Hansen 1995; Elvebakk & Hertel 1996; Convey et al. 2000; Brodo et al. 2001; Øvstedal & Lewis Smith 2001; McCarthy 2003c, 2006; Nimis & Martellos 2003; Hestmark 2004; Santesson et al. 2004; Søchting et al. 2004; Elvebakk & Bjerke 2006).

Cosmopolitan

Illustrations : Lynge & Scholander (1932: pl. III, figs 3, 4); Henssen (1970: 108, fig. 3; 123, pl. 1D, H); Martin & Child (1972: 122, pl. 34 – as Umbilicaria hyperborea); Filson (1974b: 31, fig. 8); Jahns (1980: 219, pl. 525); Thomson (1984: 288 – as Omphalodiscus decussatus); Hestmark (1990: 559, fig. 7); Sancho et al. (1992: 193, fig. 3C,D); Wei & Jiang (1993: 80, fig. 45; 81, fig. 46); Valladares (1994: 497, fig. 17); Hansen (1995: 67); St Clair (1999: 200); Brodo et al. (2001: 702, pl. 861; Øvstedal & Lewis Smith (2001: pl. 86; pl. 91).

Umbilicaria decussata is characterised by: the saxicolous habit; a monophyllous thallus, normally 2–8 cm diam. (rarely to 13 × 10 cm); the grey-brown to dark-grey, scabrid to granular-crystalline upper surface with a pattern of deep, sharp ridges radiating from the centre (above the umbilicus) and fading to weak reticulate ridges at margins; a black lower surface (single-celled thalloconidia present) with a narrow, grey to brownish marginal zone; the absence of rhizinomorphs; rather rare, small (0.5–1.5 mm diam.), sessile apothecia with convex, papillate, fissured to obscurely gyrose discs; and broadly ellipsoidal to ovoid ascospores, (8.5–)10–13 × 3.5–6 μm.