Porina multipuncta

Thallus thin, wide-spreading, smooth or somewhat sparingly rimose-cracked, or scurfy, superficial or partly immersed, effuse, dull or dark red-brown, rarely paler, becoming grey and discoloured in dried collections; soralia bright orange when fresh,usually evenly coloured with little green colour showing unless damaged, fading to pale dull cream-grey in dried collections, 0.1-0.3 mm diam., small, rounded or sigmoid, punctiform, very numerous, erose to excavate, discrete, becoming confluent or forming a minute mosaic of tiny irregular soralia; soredia very fine, 15–45 × 13–25 μm in size, photobiont partly enclosed by hyphae, fungal cells sometimes conical, giving an angular appearance to the soredia; rarely propagules arise singly on the thallus and develop into very fragile aggregations of minute granules 25–50 × 25–37 μm in size. Ascomata very rare (known from S.W. & Mid Wales), 200–280 μm diam., brown, immersed below; exciple brown, K–, orange within and K+ orange-red. Ascus with ring structure. Ascospores 16–22.5 × 3–5.5 μm. Soralia C–, K–, KC–, Pd–, UV– (no lichen products detected by TLC).

Porina multipuncta is characterised by the wide-spreading thallus studded with numerous tiny bright orange soralia; it is the only sorediate species of the genus in Britain. Young material of P. multipuncta may resemble Zwackhia sorediifera (Arthoniales: Lecanographaceae), which has a paler thallus and generally paler soralia, with the soredia coarser, more strongly green internally and C+ reddish. Thelopsis corticola (Ostropales: Gyalectaceae) and Francisrosea bicolor (Ostropales: Gyalectaceae) are C–, but both have non confluent, persistent, defined and roughly circular soralia. The former also has fine soralia but these are pale ochre with green tinges, while the latter has coarser orange and green soralia.