Porina collina

Thallus superficial, thin, light to dull greenish orange-brown, continuous or with a few cracks; isidia abundant, at first arising singly, later confluent, forming bright orange-brown patches, paler at the base giving a two tone effect, which are finely granular to densely coralloid, the individual isidia not distinguishable, soon confluent and sometimes covering much of the thallus. Isidial patches disintegrating in water into irregularly shaped granules 30–150 (–250) × 30–125 (–150) μm, hyphae sparse within the granules, not completely enclosing the photobiont cells. Perithecia black, the base immersed in the thallus, 220–420 μm diam.; involucrellum absent, exciple dark purplish brown, K+ grey to dark grey-brown to dark greenish grey, inner part yellowish, K+ intensifying. Ascus apex rounded, with thickening or a refractive ring. Ascospores 3-septate, 24–43 × 5.5–6 μm.

When perithecia are absent this can be confused with other species with vegetative propagules. Porina rosei has isidia with a distinct cortex with bulging cells, P. hibernica (with which it grows in the New Forest) has more evenly coloured and duller orange, robust isidia 30–100 μm diam. which retain traces of branching in microscopic preparations, P. pseudohibernica [a central and S.E. European species] has rather discrete isidia which are less fragile, and P. multipuncta usually has soredia although these rarely aggregate into very fragile structures which do not form discrete patches. Gyrographa gyrocarpa (on rock) and Zwackhia sorediifera (on trees) have soralia that are often a more vivid orange, and are C+ red.