Arthonia clemens
≡*Phacopsis clemens Tul., Annls Sci. nat. Bot. sér 3, 17: 124 (1852).
Description : Lichenicolous, blackening host apothecia. Apothecia developing in host hymenium and blackening the disc, 0.1–0.4 mm diam., black, rounded, flat to slightly convex. Epithecium dark-brown, K+ olivaceous. Hymenium to 50 μm tall, colourless, I+ blue. Hypothecium colourless or pale brownish. Paraphysoids 1.5–2 μm diam, apices with dark-pigmented apical caps, 2–4 μm diam. Asci clavate, ovoid or pyriform, 25–50 × 10–18 μm. Ascospores narrowly ovoid to soleiform, colourless, 9–15 × 3–5 μm.
N: ? Easily overlooked and probably more widely distributed. A widespread lichenicolous fungus known from Europe, Greenland, Asia, North America, North Africa (Hawksworth 1983a; Alstrup & Hawksworth 1990; Triebel et al. 1991; Nimis 1993; Hafellner et al. 2002; Nimis & Martellos 2003).
Cosmopolitan
Hosts : Lecanora dispersa, L. polytropa, Protoparmelia badia, Xanthoria parietina. See also Vouaux (1914a: 149).
Illustration : Hawksworth (1983a: 37, fig. 8).
* Arthonia clemens is characterised by: the lichenicolous habit; black apothecia, 0.1–0.4 mm diam., developing on host apothecia; and narrowly ovoid to soleiform ascospores, 9–15 × 3–5 μm. It occurs on the apothecia of many different crustose lichens, the host apothecia becoming deformed and covered by the parasite's aggregated black apothecia. It is common on the apothecia of species of Lecanora and especially the L. dispersa group. It was recorded in New Zealand from discs of Xanthoria parietina (Kondratyuk & Galloway 1994: 26). [According to Grube & Matzer (1997) this name must be used exclusively for material confined to Rhizoplaca, with species growing on Lecanora belonging to several distinct species.]
