Punctelia reddenda (Stirt.) Krog

    Thallus foliose, rosette-forming, 3-6 cm diam., lobes 5-10 mm wide, sometimes with small folioles, upper surface grey-green, green-yellowish, olivaceous, pseudocyphella punctiform from where arise soralia with granular soredia, or more precisely isidiomorphs, lacerate, ascending, lower surface blackish paler towards the margin. Apothecia unknown in our prospection area. Photobiont: Trebouxioid. Cortex : K+ yellow, KC+ yellow ; Medulla : C-, K-, KC-, Pd-, UV-.  Rather common, on trunks of trees in humid woodlands under oceanic climate influence (in the Lobarion), and also on ornament trees in gardens or parks near the seashore (There is a reduced size form occurring on the twigs of Abies in very humid forests: Punctelia reddenda forme ramicole).

_ This species is close to Punctelia borreri of which it differs by the C- reaction and the presence of isidiomorphs and its more green-yellow colour when moist.

N.B. Not to be confused with some corticolous forms of Parmelia saxatilis with authentic isidia, cortex K+ yellow and medulla K+ orange > red, Pd+ orange.