Candelaria concolor
An locally common and increasing lichen in the south of nutrient enriched habitats, forming small delicate yellow intricate patches, often in the branch axils and rain tracks of tree trunks.. Thallus greenish-yellow to lemon yellow forming small, discrete, roughly circular cushions less than 1 cm across. These may coalesce or appear as scattered fragments. Minute lobes are up to 1 mm long, thin and with toothed margins. The edges and occasionally the whole thallus may be coarsely granular. Apothecia are rare, up to 1 mm wide, dirty yellow with a roughened margin.
Thallus typically forming small, discrete suborbicular cushions <1 cm across, irregularly spreading, sometimes coalescing or in scattered fragments, ± closely appressed, occasionally dissolved into coarse, ascending granules; lobes flattened, finely divided, ca 1 mm long, 0.2–0.5 mm broad, the surface flat or ± wavy, often somewhat raised and fan-like, the margins distinctly crenulate, ± overlapping, entire, often becoming blastidiate or coarsely sorediate, bright yellowish green to chrome-yellow above; lower surface corticate, matt, almost white beneath; rhizines scattered, unbranched, white. Apothecia 0.4–1 mm diam., rare; disc dull greenish-orange or pale brownish-yellow; thalline margin smooth, becoming ± uneven-granular with age, concolorous with the disc. Ascospores 6–14 × 4–6 μm, aseptate but biguttulate. Conidiomata pycnidia, ca 100 μm diam., rare; conidia 1.8–2.7 × ca 1 μm. Thallus C–, K–, KC–, Pd–, UV± dull orange.
Irregular cushions may resemble Xanthoria ulophyllodes or and X. candelaria which is less delicate in appearance and have a deeper orange, K+ purple thallus. Candelaria pacifica is similar but is generally smaller and has a cobweb-like lower surface and few, if any, rhizines.
Also see Species Description PDF, Fungi of Great Britain and Ireland & high quality images by Norbert J. Stapper at link, comparing both Candelaria concolor & C. pacifica.
On nutrient-rich bark of well-lit, wayside broad-leaved trees, especially Acer, Fraxinus, Salix and Ulmus, also on wooden fences, occasionally on nutrient-enriched rocks and walls; local but spreading, likely due to its tolerance for nitrogen.
Throughout Britain and Ireland but more common in the south.
Cannon, P., Coppins, B., Orange, A., Sanderson, N. & Simkin, J. (2021). Candelariales: Candelariaceae, including the genera Candelaria and Candelariella. Revisions of British and Irish Lichens 21: 1-8. Link.
Stapper, N. J. (2012) Bestimmungshilfe zur Unterscheidung von Candelaria concolor und C. pacifica 1. Illustrierte Bestimmungshilfe zur Unterscheidung von Candelaria concolor und Candelaria pacifica. Archive for Lichenology. 7 Link.
Text by Neil A Sanderson based on Cannon et al (2021)