Flora of New Zealand Series

≡Opegrapha radiata Pers., Ann. Bot. (Usteri) 1: 29 (1794).

=A. subramulosa Müll.Arg., Bull. Herb. Boissier, 2. App.1: 83 (1894).

≡Arthonia ramulosa C.Knight & Mitt., Trans. Linn. Soc. 23: 105 (1860) non Nyl. [Mém. Soc. Natn. Sci. nat. Cherbourg 2: 335 (1854)].

Arthonia ramulosa.[sensu Knight & Mitten.] Lectotype: New Zealand. Sine loco [probably Auckland], 1858, Charles Knight 172 – BM [fide Galloway (1985a: 13)].

Description : Thallus immersed, usually delimited by a brown or brown-black prothalline line and often mosaic-forming, whitish, pale-grey, sometimes with a brownish or olivaceous tinge. Apothecia variable, rounded, elongate to stellate, 0.2–0.8 mm diam., linear to sparingly branched or stellate and to 1–2 × 0.1–0.2 mm, flat to subconvex, black, epruinose. Hymenium 35–50 μm tall, colourless; epithecium brown or olivaceous, K+ greenish. Hypothecium 10–25 μm thick, colourless to pale olivaceous, K+ greenish. Paraphysoids numerous, 1–2 μm thick, apices slightly swollen to 3–4 μm diam., with brown apical caps. Asci broadly clavate. Ascospores obovoid to oblong, 3-septate, apical cell not enlarged, 15–20 × 4.5–6 μm.

N: Auckland (sine loco), Wellington (Wellington City). S: Canterbury (Mt Palm, Lowry Peaks Ra., Peel Forest). On smooth-barked trees (e.g. Acer pseudoplatanus) in parks and gardens, and on Cytisus scoparius and Discaria toumatou more widely in the countryside (Polly 1994). A pioneer species on smooth bark of deciduous trees and known from Great Britain, Europe, Scandinavia, North America and Australia (Purvis et al. 1992; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Sundin & Tehler 1998; Scholz 2000; McCarthy 2003c; Nimis & Martellos 2003; Santesson et al. 2004).

Cosmopolitan

Illustrations : Knight & Mitten (1860: pl. XII, fig. 32 – as Arthonia ramulosa); Galløe (1972: p. 47, pls 35, 170); Moberg & Holmåsen (1982: 218); Foucard (1990: fig. 21); Purvis et al. (1992: 661, fig. 33O); Dobson (1992: 53; 2000: 61; 2005: 69); Letrouit-Galinou et al. (1994: 413, fig. 12; 415, fig. 14D); Wirth (1995a: 136, fig. 23A; 1995b: 137); Boqueras (2000: 75, fig. 8G); Brodo et al. (2001: 165, pl. 116).

Arthonia radiata is characterised by: the corticolous habit; the pale grey-white to brownish thallus, delimited by a thin black line of prothallus and forming mosaics on bark; black, elongate to branched apothecia in star-like clusters; and 3-septate ascospores, the apical cell not enlarged.