Arthothelium lirellans
Dermatina swinscowii
A non-lichenised fungus of temperate rainforest, which gives a pale discolouration to the bark, with irregularly rounded to bluntly stellate lirellae. Easily overlooked in the field for Naevia punctiformis, and microscope examination is required to confirm it is not N. punctiformis and also to separate it from the similar Arthothelium orbilliferum.
Thallus immersed, usually delimited by a brown line, indistinct but discolouring bark whitish, dull yellowish, fawn or pale grey to grey-brown; photobiont absent. Apothecia to 0.8 mm diam., or 0.3–1.2 × 0.1–0.3 (–0.5) mm, shortly elongate, irregularly rounded or polygonal, sometimes slightly branched or bluntly stellate, in section 45-60 µm tall; epithecium green-brown, K+ greenish; hymenium 35–40 µm tall, colourless; hypothecium indistinct or to 15 µm tall, colourless; paraphysoids 1–2 µm diam., butpigmented and to 3 µm diam. in the epithecium, apices often with dark caps. Ascospores 17–27 (–30) × 8–12 µm, cylindric-obovoid, muriform with (4–) 5 to 8 transverse septa and 0–4 transverse cells with a single longitudinal septum. Pycnidia 60–80 µm diam., rare, the wall brown, K+ greenish; conidia 3.5–5 × 0.5–0.7 µm, bacilliform.
Easily overlooked in the field for Naevia punctiformis; in oceanic woods look out for more irregular to somewhat stellate lirellae on more dicoloured and paler bark as candidates, but microscope examination is needed to determine the species. Close (in morphological terms at least) to A. orbilliferum, which has more obovoid-ellipsoid spores.
On smooth bark (Hazel, Holly, Oak, Rowan), often on branches, in old woodlands (especially in ravines), in the temperate rainforest zone.
West Britain and Ireland, frequent in west Scotland, rare beyond and not yet found in Wales.
A small non-lichenised species, found on twigs or small stems in oceanic woodland. Very rare outside of the core area of temperate rainforests of the western Highlands and the inner Hebrides. Outside of the Highlands, vulnerable to loss to habitat deterioration, mainly from under grazing.
Britain: Notable & International Responsibility species
Scotland: Priority Taxon for Biodiversity in Scotland
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.
Text by Neil A Sanderson, based on Cannon et al (2020)