Xanthoparmelia conspersa
Thallus 1-6 (-10) cm diam., forming rosettes or coalescing into larger patches or of ± scattered or radiating lobes, closely appressed. Lobes (1-) 2-4 mm wide, slightly broadened towards the ends, discrete, contiguous or overlapping, margins often indented, not raised. Upper surface yellow-grey, ± shining, smooth, isidiate. Isidia mostly numerous, occasionally very sparse, laminal, globose and constricted at base or usually cylindrical, simple or branched, coralloid, scattered or ± continuous, especially on older parts of the thallus. Lower surface jet-black, with short, simple rhizines.
Anamorph: conidiomata pycnidia. Conidia 4-5 × 1 μm, cylindrical.
Teleomorph: ascomata apothecia, occasional; disc to 1 mm diam., concave, becoming flat and undulating with age, red-brown. Thalline exciple thin, crenulate, ± inflexed, ± isidiate. Ascospores 6-10 × 4-5 μm.
Chemistry: cortex K–; medulla C–, K+ yellow-orange, KC+ orange-red, Pd+ orange, UV– (usnic, stictic [major], constictic, norstictic and cryptostictic acids [all minor]).
Assessed by Woods & Coppins as of Least Concern.
The form and abundance of the isidia can be very variable, ranging from short, rounded and constricted at the base, to thin, crowded, coralloid, cylindrical and forming a dense, coarsely areolate crust, ± obscuring the thallus, or lacking altogether in which case the specimen is often richly fertile.
Xanthoparmelia tinctina has globose isidiawhich are often flattened at the top or occasionally are erupting at the tips and has salazinic acid (major) in the medulla. X. protomatrae always lacks isidia and has fumarprotocetraric acid (Pd+ rust-red) in the medulla.
Common in SW, W & N British Isles, rarer in the E, fairly tolerant of air pollution and on the increase. BLS map here.
A saxicolous species of well-lit, siliceous rocks, often slightly nutrient-enriched, walls, memorials and roof tiles, also in water-seepage tracks, rarely on hard lignum and acid-barked trees in coastal and inland sites.