Arthonia anglica

The thallus is mainly embedded in the outer bark (endophloeodal), grey-white to pale fawn, and forms circular to elliptic patches at least 6×3 cm, each bounded by a dark brown hypothalline line. In microscopic preparations the hyphae stain blue with iodine. Standard spot tests on the thallus are negative (K−, C−, KC−, PD−, UV−). The apothecia are numerous and often crowded, forming elongated, slit-like structures (lirellae) that are usually irregularly star-shaped (substellate), only occasionally neatly stellate, and reaching up to 12 mm across in the largest aggregates. The individual "arms" are narrow (about 0.08–0.16 mm wide) and pale to dark reddish-brown, without pruina. Microscopically, the apothecia are 80–130 μm tall. The epithecium is reddish-brown and turns olivaceous with K, while the hymenium is hyaline and iodine-positive (I+ blue). The asci are clavate and eight-spored, with only a minute amyloid ring at the apex, and the ascospores are typically 17–24×6–8 μm, 3–4-septate, and macrocephalic (with the upper cell larger than the lower). North American collections have been reported with slightly smaller spores, about 15–22 × 5–7 μm, while retaining the same general spore form and chemistry. Spores are hyaline and smooth when young, but older spores develop brown, granular warting. Pycnidia have not been observed. …

In Britain, Arthonia anglica has been found on the bark of mature trees in long-established woodland, recorded from trunks or main branches of beech (Fagus) and holly (Ilex). The few known gatherings include material from southern England, with a modern collection reported from North Devon on holly in cliff woodland, and an older record from the New Forest area on holly. In Spain, A. anglica has been reported from Galicia, where it was collected on Alnus glutinosa and represents the first record for the Iberian Peninsula. The only earlier Spanish report was from La Gomera in the Canary Islands. In eastern North America, A. anglica has been recorded mainly from humid, mesic hardwood forests, especially in streamside woodlands in the Ozark region. It has been collected on the bark of hardwoods including maple (Acer) and hornbeam (Carpinus), and has also been found at middle to low elevations in the southern Appalachian Mountains as well as in the coastal plain and piedmont of the southeastern United States. It has also been recorded in Virginia and Wisconsin. The species appears to have a very southern British distribution and has so far been confirmed from only a small number of collections. …