Arthonia ilicinella
A rare species of high quality oceanic woodland, typically in Atlantic Hazel woods in the western Scottish temperate rain Forests, but mainly on old Holly in Ireland and southern England. Similar to Arthonia ilicina, but distinguished by the smaller apothecia and ascospores. Potential thalli can be spotted in the field by the apothecia being smaller, more irregular and broken up compared to the larger and more rounded A. ilicina apothecia, but examination under a microscope is required to confirm this lichen.
Thallus immersed, effuse or delimited by a brown line, white-grey or cream-white. Apothecia 0.1–0.6 mm diam., or elongated to ca 0.8 × 0.15–0.3 mm, irregularly rounded, ± flat, black, not pruinose, 80–95 μm tall; epithecium red-brown, K+ pale green; hymenium 40–60 μm tall, pale red-brown, K+ pale pale green; hypothecium 10–25 μm tall, concolorous with the hymenium; paraphysoids ca 1 μm diam., brown- walled and 1.5–2 μm diam. in the epithecium, sometimes a few with apical caps. Ascospores (16–) 18–23 × 7–9 μm, cylindric-obovoid, 3- or 4(–5)-septate, the apical cells enlarged; when old becoming brown, smooth or very faintly warted (×1000). Pycnidia often present but usually few, 60–80 μm diam., the wall red-brown, K+ pale green; conidia 7–9 × ca 1 μm. Lichen products not detected by TLC.
Closely related to Arthonia ilicina, but distinguished by the smaller apothecia and ascospores. A. stellaris has ± stellate apothecia, and ascospores that become distinctly warted (×400) when brown. Potential thalli can be spotted in the field by the apothecia being smaller, more irregular and broken up compared to the larger and more rounded A. ilicina apothecia.
On smooth bark, especially of Hazel and Holly, once observed as being parasitic on A. ilicina. Mainly found in temperate rainforests but with rare occurrences in drier southern oceanic woods.
Rare, W. Scotland (Argyll to Skye, W. Ross), W. Ireland, N. Wales, W. & S. England (Lake District, Cornwall & New Forest).
A rare species of oceanic woodland, typically in Atlantic Hazel woods in the western Scottish temperate rain Forests, but mainly on old Holly in Ireland and southern England. Dependant on the maintenance of high quality extensive Atlantic woodland.
Britain: Near Threatened
Scotland: Priority Taxon for Biodiversity in Scotland
Wales: not assessed but known only from a single site, where it was recorded in 2016
England: very rare recorded from four sites
Cannon, P., Ertz, D., Frisch, A., Aptroot, A., Chambers, S., Coppins, B. J., Sanderson, N. A., Simkin, J. & Wolseley, P. (2020) Revisions of British and Irish Lichens Volume 1 August 2020 Arthoniales: Arthoniaceae. BLS
Text by Neil A Sanderson, based on Cannon et al (2020)