Caloplaca cerina
A striking lichen, readily identified by the frequently flexuose apothecia with orange to green-yellow discs on a thick, pale to dark grey, often tinged glaucous or blue thallus. An epiphyte found on high pH and nutrient rich habitais. Its distibtion has been reduced in extent by past acidifying air pollution, however, recent signs of recolonisation have been noted.
Thallus crustose, pale to dark grey, often tinged glaucous or blue, usually rather thick, occasionally immersed and inconspicuous, continuous, somewhat waxy, the surface smooth or rarely warted; prothallus pale or absent. Apothecia to 1.5 (–2) mm diam., scattered to contiguous, sometimes overlapping, often angular, sessile, constricted at the base; thalline margin persistent, even, swollen, raised, flexuose, grey; discs orange, orange-yellow or green, concave when young but becoming flat when mature; paraphyses broadening towards the tips, to 4 µm diam. Ascospores 12–15 × 7–9 µm, ellipsoidal, septum 5–8 µm thick, about 1/3–1/2 of the length of the ascospore. Thallus and thalline margin K–; discs K+ purple.
Readily identified by the frequently flexuose apothecia with orange to green-yellow discs, concave when young, surrounded by a distinctive persistent smooth grey thalline margin. C. chlorina and C. virescens are closely related but they reproduce asexually and are infrequently fertile. Sanguineodiscus haematites could be mistaken for Caloplaca cerina, but that has brown-red rather than orange apothecial discs. A polymorphic species that may contain several cryptic segregates, according to Šoun et al. (2011).
On bark and twigs, sometimes on wood, especially with a high pH (Sycamore, Aspen, Ash, Elder, Elm), or where affected by nutrients, also overgrowing mosses and plant debris over base-rich rocks and earth, rarely directly on calcareous rocks.
Formerly frequent throughout Britain and Ireland, now decreased and rather rare in polluted habitats, but shows signs of recovery in some less severely impacted areas.
The distribution, with concentrations in the eastern Highlands and the south west of England along with areas between with an absence of records or of mainly old records, points to large scale losses to acidifying air pollution in the past. Recently, however, signs of recolonisation have been noted.
Cannon, P., Arup, U., Coppins, B., Aptroot, A., Sanderson, N., Simkin, J. & Yahr, R. (2024). Teloschistales, including Brigantiaea (Brigantiaeaceae), Megalospora (Megalosporaceae) and Amundsenia, Athallia, Blastenia, Calogaya, Caloplaca, Cerothallia, Coppinsiella, Flavoplaca, Gyalolechia, Haloplaca, Huneckia, Kuettlingeria, Leproplaca, Marchantiana, Olegblumea, Polycauliona, Pyrenodesmia, Rufoplaca, Rusavskia, Sanguineodiscus, Scythioria, Solitaria, Squamulea, Teloschistes, Variospora, Xanthocarpia, Xanthomendoza and Xanthoria (Teloschistaceae). Revisions of British and Irish Lichens 43: 1–75.
Šoun, J., Vondrák, J., Søchting, U., Hrouzek, P., Khodosovtsev, A. & Arup, U. (2011). Taxonomy and phylogeny of the Caloplaca cerina group in Europe. Lichenologist 43: 113–135.
Text by Neil A Sanderson based on Cannon et al (2024)