Phaeographis smithii
Similar to Phaeographis dendritica, with also with a white thallus, but with usually with shorter and less branched appothecia that rarely radiating out from the centre. Confirmed by a vertical cut across the apothecia, which shows this species to lack the dark tissue below the hymenium seen in P. dendritica. The most widespread Phaeographis, also south western in distribution but extending into west Scotland. Also colonises more rapidly than the other Phaeographis species and is more typical of twigs than P. dendritica, especially where their ranges overlap.
Like Phaeographis dendritica but with a smoother, continuous, only sparingly cracked thallus. Apothecia usually shorter, less branched, rarely radiating; thalline margin inconspicuous; true exciple colourless or absent at the base; hymenium 80–100 µm tall. Ascospores 25–40 × 7–9.5 µm, 5-to 7-septate. Thallus C–, K+ yellow→ red crystals), KC+ red, Pd+ orange (reactions often patchy), UV– (norstictic and connorstictic acids).
A vertical cut across the apothecia is sufficient to show the lack of excipular tissue below the hymenium compared to the dark tissue seen in P. dendritica. This can be done on damp material in the field with a good lens (×20 best).
Along with P. dendritica, host to Tremella phaeographidis Diederich et al. (1996), likewise to a taxon close to Arthonia graphidicola in N. Cornwall.
On mainly smooth bark of broad-leaved trees and shrubs, more rarely on conifer branches, in moderate shade; usually in woods. More typical of twigs than P. dendritica, especially where their ranges overlap.
W. Britain, rare in Scotland but with scattered records north to W. Ross; throughout Ireland. Recolonising rapidly into areas of lowland England, where it was lost in the 20th century to pollution and appearing in totally new areas such as S.E. Scotland, potentially the latter could be reflecting warmer temperatures.
Aptroot, A., Weerakoon, G., Cannon, P., Coppins, B., Sanderson, N. & Simkin, J. (2023). Ostropales: Graphidaceae, including the genera Allographa, Clandestinotrema, Crutarndina, Diploschistes, Fissurina, Graphis, Leucodecton, Phaeographis, Schizotrema, Thelotrema and Topeliopsis. Revisions of British and Irish Lichens 36: 1-23.
Text by Neil A Sanderson based on Aptroot et al (2023)