Flora of New Zealand Series

≡Arthonia obtusula Nyl., Lich. Nov. Zel.: 123 (1888).

Lectotype: New Zealand. Sine loco [probably Wellington], Charles Knight – H-NYL 5728 [fide Makhija & Patwardhan (1995a: 208)].

Description : Flora (1985: 19). See also Makhija & Patwardhan (1995a: 208–210).

N: Known only from the type collection.

Endemic

Arthothelium obtusulum is characterised by: the corticolous habit; greenish white to grey, smooth to verruculose thallus; blackish brown apothecia, rounded to ±oblong or orbicular, covered by thallus or naked, 0.3–0.5 mm diam.; epithecium dark blackish brown, 6–13 μm thick; pale-brown to colourless hymenium, 35–130 μm tall, I+ blue; hypothecium pale-brown; asci bitunicate, pyriform-obovate; ascospores 8 per ascus, colourless, oblong, muriform, 3–6 septate, with a large undivided, terminal cell with the remainder of the cells divided vertically by 1–3 septa, 20–30 × 6–9 μm. The Australian species A. polycarpum Müll.Arg., is shown to be identical to A. obtusulum (Makhija & Patwardhan 1995a: 210).