Flora of New Zealand Series

Holotype: New Zealand. Nelson, Sharland Creek, on siliceous rock in lowland mixed Nothofagus– podocarp forest, 160 m, 12.v.1993, W. Malcolm 851 – CHR 413972.

Description : Thallus crustose, continuous to areolate, areolae angular, 0.5–0.7 mm diam., ashy grey-green, bounded at the margins by a whitish grey prothallus. Apothecia rounded, lobed or aggregated and then deformed through mutual pressure, 0.75–1 mm diam., 0.2–0.5 mm tall, base partly immersed in thallus; disc black, plane to subconvex, epruinose, margins cobwebby, greyish white. Exciple barely developed laterally, to 50 μm wide, hyphae free, hyaline, 2 μm thick, interwoven, without scattered crystals. Hymenium 70–75 μm tall, colourless, with sparse scattered granules; epithecium pale-green. Hypothecium red-brown, 100–150 μm thick. Asci cylindrical-clavate, (4–6)–8-spored. Ascospores cylindrical, apices rounded, transversely (5–)7-septate, constricted at septa, halonate, (22–)25–28(–30) × 4–4.5 μm.

S: Known only from the type locality.

Endemic

Illustrations : Malcolm & Vězda (1995a: 361, fig, 2); Malcolm & Galloway (1997: 130).

Byssoloma octomerum is characterised by: the saxicolous habit; the ashy grey-green, areolate thallus delimited by a whitish grey prothallus; plane to subconvex, epruinose, black apothecia with cobwebby, greyish white margins; and (5–)7-septate, halonate ascospores, constricted at septa, (22–)25–28(–30) × 4–4.5 μm.