Arthonia santessoniana
Description : Lichenicolous, commensalistic or weakly parasitic on species of Pseudocyphellaria. Apothecia scattered, black to occasionally dark-brown, rounded to somewhat irregular in outline, superficial. lecideoid to to somewhat fleck-like, c. 0.08–0.3 mm diam., c. 55–75 μm tall in section. Epithecium 5–10 μm thick, dark-brown becoming greenish black in K. Hymenium 25–30 μm tall, colourless, I+ red, K/I+ blue. Hypothecium 20–25 μm thick, pale reddish brown. Paraphysoids 1.5–3 μm thick in hymenium, hyaline; in epithecium brown-walled, richly branched and extending periclinally above asci; apices not distinctly thickened, 2–3 μm diam. Asci broadly clavate, 23–35 × 14–19 μm, with a distinctly amyloid ring in K/I, 8-spored. Ascospores colourless, 1-septate, constricted at septum, ellipsoidal to oblong-ovoid, upper cell usually somewhat wider than the lower, 11–14 × 4.5–6 μm, with a thin (less than 0.5 μm) perispore. Pycnidia not seen.
S: Canterbury (Boyle River near Lewis Pass). Only collected once in New Zealand, but probably more widely distributed. Known also from Lago Fagnano, Argentinian Tierra del Fuego (Wedin & Hafellner 1998: 81).
Austral
Hosts : Pseudocyphellaria fimbriata, P. montagnei.
Illustrations : Wedin & Hafellner (1998: 77, fig. 6D; 79, fig. 7C).
* Arthonia santessoniana is characterised by: the lichenicolous habit (species of Pseudocyphellaria as host); the scattered black to dark-brown superficial, lecideioid apothecia; 1-septate, colourless ascospores, 11–14 × 4.5–6 μm, constricted at septum.
