Porpidia platycarpoides
Thallus usually granular-areolate, whitish or ashy grey. Areoles ± convex, surface irregularly lumpy, minutely papillate or verrucose, the cracks between areoles narrow to gaping. Medulla I–. Prothallus inconspicuous, or thinly developed at the thallus edge. Soredia and isidia absent. Photobiont chlorococcoid.
Anamorph: no information available.
Teleomorph: ascomata apothecia, large, 0.5-3 mm diam., scattered, sessile to slightly immersed. Disc black, matt or often thinly white-pruinose, occasionally ± umbonate at maturity, flat to convex. Thalline exciple absent. True exciple prominent, raised, swollen, sometimes convoluted, often shiny; exciple hyphae 4-8 μm diam. Epithecium olive-brown. Hymenium 120-185 μm tall, hyaline, I+ blue. Interascal tissue of paraphyses, septate, branched-anastomosing, netted, slightly swollen at the apices. Asci ± cylindrical, Porpidia-type, 8-spored. Ascospores 15-23 (-26) × 7-10 (-12) μm. , ellipsoidal, aseptate, hyaline, thin-walled, with a well-developed perispore.
Chemistry: medulla C–, K+ yellow to red (acicular crystals), Pd+ yellow (norstictic, connorstictic acids and 2 unidentified compounds).
Assessed by Woods & Coppins (2012) as of Least Concern.
Close to Porpidia macrocarpa but differs in the white epilithic thallus, K+ red (acicular crystals) reaction and, more frequently, pruinose apothecia. The less regularly areolate thallus, taller hymenium and larger ascospores separate this species from Lecidea lactea, which also has a K+ red thallus.
Scattered throughout western W Britain in both coastal and inland sites, also in maritime habitats in SE and E Scotland and NE England. BLS map here.
On siliceous rocks and compacted soil, generally coastal but sometimes inland, especially on basalt.