Flora of New Zealand Series

Description : Lichenicolous. Thallus small, 0.3–1 cm diam., rounded, areolate without a distinct prothallus, parasitising central parts of Sporastatia testudinea. Areolae 0.2–0.6 mm diam., usually 0.2–0.4 mm thick, angular to rounded, plane to subconvex, whitish-yellow to yellow, surface slightly farinose, matt. Apothecia angular to rounded, 0.3–0.7(–1) mm diam., disc plane to convex, without a distinct margin. Epithecium densely granular, 8–13(–15) μm thick, dark brownish or purplish K+ reddish or −. Hymenium colourless to brownish, 70–100 μm tall. Hypothecium brown, 100–200 μm thick. Asci clavate, 69–80 × 15–20 μm, 8-spored. Ascospores 1-septate, bluish brown to dark olive-brown, 9–14 × 4–6(–7) μm, slightly constricted at septum.

Chemistry : Thallus K−, C−, KC−, Pd+ yellow; containing rhizocarpic and psoromic acids.

S. Canterbury (Malte Brun Ra., Liebig Ra., Mt Sepastopol), Otago (Old Man Ra., Gem Lake Umbrella Mts). On greywacke outcrops and shingle, and on hard quartz in high-alpine habitats (Fryday 2000a: 39), parasitic on thalli of Sporastatia testudinea (q.v.). Associating with Buellia aethalea and brown species of Xanthoparmelia. Known also from the European Alps, Scandinavia, Greenland, Svalbard, North America and the Himalaya (Runemark 1956b; Hertel 1975b, 2001; Hansen 1982; Timdal & Holtan-Hartwig 1988; Poelt 1990; Nimis 1993; Santesson 1993; Hansen 1995; Esslinger & Egan 1995; Elvebakk & Hertel 1997; Thomson 1997; Fryday 2000a; Nimis & Martellos 2003; Feuerer & Timdal 2004; Santesson et al. 2004).

Bipolar

Illustrations : Runemark (1956a: fig. 13E, F; 51, fig. 13B; 52, fig. 14C, L); Hansen (1982: 29, fig. 17; 1995: 113).

* Rhizocarpon pusillum is characterised by: the lichenicolous habit; the small yellow-green thallus without a black, marginal prothallus, parasitic on Sporastatia testudinea; and 1-septate, bluish brown to dark olive-brown ascospores, 9–14 × 4–7 μm; and rhizocarpic and psoromic acids in the medulla.