Flora of New Zealand Series

Holotype: New Zealand. Campbell I., rock outcrops at summit of Mt Azimuth, 488 m, 3.i.1970, H.A. Imshaug 46561 – MSC. Isotypes CHR, E.

Description : Thallus orange-red, 0.05 mm thick, areolate. Areolae flat, 0.4–0.6 mm diam., usually contiguous. Apothecia black, lecideine, orbicular, 0.4–0.6 mm diam., sessile, disc concave, margin thick, raised, persistent, 0.1 mm wide, often radially cracked. Epithecium very pale-blue, 15–20 μm thick. Hymenium colourless, 90–100 μm tall, I+ blue. Paraphyses relatively thick, 2.0–2.5 μm wide, sparingly branched and anastomosing, apices slightly swollen, to 3.5 μm wide, with a brown cap. Hypothecium thick, dark-brown, carbonaceous . Asci cylindrical, 70–85 × 17–25 μm. Ascospores 1-septate, hyaline becoming brown when over-mature, 18–21(–24) × 9–12 μm, halonate. Pycnidia not seen.

Chemistry : TLC−, all reactions negative.

A: (Mt Eden, Cloudy Peak). C: (Mt Lyall, Mt Azimuth, Mt Dumas). On subalpine to alpine rocks in fellfield, 350–566 m, associating with Fuscidea subasbolodes, Lecidea lygomma, Rimularia maculata and species of Placopsis (Fryday 2004a).

Endemic

Rhizocaron oxydatum is characterised by: the orange, areolate thallus; sessile, black apothecia; the carbonised exciple and medium-sized, 1-septate ascospores. It is similar to R. hochstetteri, differing in the colour of the thallus and in the carbonised exciple. Recent molecular studies (Ihlen & Ekman 2002) have shown R. hochstetteri to occupy a rather isolated position in the Rhizocarpaceae, being more closely related to the genus Poeltinula than to other species of Rhizocarpon. The carbonaceous exciple of R. oxydatum appears to place it in an intermediate position between R. hochstetteri and Poeltinula (Dr A. Fryday, pers. comm.).