Opegrapha atra
Description : Thallus thin, smooth to effuse or delimited in small patches, often forming mosaics, whitish, greyish or olivaceous. Apothecia lirelline, black, carbonised, short, 0.5–2 × 0.1–0.3 mm, and to 130 μm tall, abundant, in dense clusters or randomly distributed in parallel, sometimes forming dense, contiguous black patches, sessile, disc a slit. Exciple K+ olive-green. Hymenium 60–90 μm tall, I+ blue; epithecium brown or green-brown, K+ olive-green. Ascospores 3-septate, ellipsoidal to clavate, 13–18(–20) × 2.5–4(–5) μm.
Chemistry : TLC−, all reactions negative.
N: Northland (Whangarei, Warkworth), Auckland (Auckland City), South Auckland (Glenbrook, Hamilton, Huntly), Taranaki (New Plymouth), Wellington (Hutt Valley). S: Canterbury (Christchurch City). On mainly introduced trees in parks and streets, most common in rather heavily polluted urban sites. Known also from the United Kingdom, Europe, North America, Brazil, Hawai'i and Australia (Jahns 1980; Pentecost & James 1992; Nimis 1993; Esslinger & Egan 1995; Elix & McCarthy 1998; Diederich & Sérusiaux 2000; Scholz 2000; Hafellner & Türk 2001; Llimona & Hladun 2001; Aproot 2002e; Nimis & Martellos 2003; McCarthy 2003c, 2006).
Cosmopolitan
Illustrations : Jahns (1980: 251, pl. 646); Moberg & Homåsen (1982: 217); Phillips (1987: 164); Wirth (1987: 303; 1995a: 625); Letrouit-Galinou et al. (1994: 403, fig. 2; 414, fig. 13E); Boqueras (2000: 292, fig. 47A, B); Dobson (2000: 247; 2005: 289).
Opegrapha atra is characterised by: the corticolous habit; the mosaic-forming thallus; short, black lirellae in dense clusters; 3-septate ascospores, 13–18(–20) × 2.5–4(–5) μm; and no secondary chemistry.
