Porina atlantica
Porina heterospora auct. brit.
Porina nucula auct. brit.
Porina rhodostoma auct. brit.
A very rare southern oceanic species in Ireland and Britain, where it is known from temperate rainforests in south west Ireland and a single ravine in North Wales. Mainly found on base rich bark on old Oaks but rarely also rock. An orange-brown isidiate species similar to Porina hibernica, Porina rosei and Coenogonium confusum. Porina atlantica differs from these species in the thicker and taller more branched isidia than these species, with a cortex which has numerous strongly projecting cells and the rough thallus surface with convex lumps.
Thallus superficial, pale brownish cream, often with lightly convex areas separated by furrows; isidia present, orange-brown, discrete or crowded, isodiametric when young, soon ± cylindrical, branched and coralloid, fragile, to 0.5 mm high, branches 50-80 μm diam., appearing papillose under the microscope, with a cortex which has numerous strongly projecting cells; perithecia frequent, mostly immersed (in Irish material) to prominent, apex light reddish brown; involucrellum containing numerous large crystals, orange(Porina-yellow); exciple yellow. Ascus apex rounded, without a ring structure. Ascospores 6- to 9 (-10)-septate, 56–66 × 11–14 μm.
Sterile material can be distinguished from P. hibernica by the larger branched isidia with a papillose surface and the convex lumpiness of the thallus surface. Porina rosei is more similar but has thinner isidia, with less projecting cortex cells and a smooth thallus.
On base-rich bark of Quercus, sometimes overgrowing bryophytes, rarely rock.
Very rare. S.W. Ireland (N. Kerry, W. Cork, Limerick), N Wales (Merioneth).
Not assessed in Britain but likely to be rare and very threatened.
Orange, A., Cannon, P., Malíček, J., Sanderson, N., Coppins, B. & Simkin, J. (2021). Ostropales: Porinaceae, including the genus Porina. Revisions of British and Irish Lichens 4: 1-12.
Text by N A Sanderson, based on Orange et al (2021)