Peltigera leucophlebia

Thallus forming patches to 20 (–25) cm diam.; lobes 2–4 cm broad, rounded; margins often distinctly wavy, crisped, flat to ± ascending and irregularly divided; upper surface bright green when wet; photobiont green (Coccomyxa); pale grey or tinged brown when dry, smooth or indented, ± erect-tomentose near margin, smooth at the centre, with brown appressed convex wart-like cephalodia (with Nostoc), to ca 1.2 mm diam. that are not easily detached; lower surface with a distinct network of veins, brown-black towards the centre, paler at the margins, with correspondingly pale or dark simple rhizines. Apothecia rather rare, round or saddle-shaped, on short extensions from the lobe margins, fertile lobes partly corticate or wholly decorticate on the underside beneath the apothecia. Ascospores 47–80 × 5–6 µm, 3- to 7-septate, colourless or pale brown. Thallus with tenuiorin, methyl gyrophorate, ± gyrophoric acid (C+ red), 4 unidentified triterpenes (only one of which is common to P. britannica).

Characterised by the bright green colour when wet, large rounded lobes, the appressed cephalodia on the upper surface which are difficult to remove and the distinct network of dark brown veins on the underside of older parts of the thallus. See Peltigera britannica, which is similar but the cephalodia are concave, sessile and easily detached and it has only indistinct veins on the underside.

Peltigera leucophlebia is a polyphyletic and highly diverse taxon that appears to contain a number of segregate taxa (Pardo-De La Hoz et al. 2018), but British and Irish material was not included in their study so its significance is unclear for our region. It may be separated from the non-British P. aphthosa by the ± decorticate undersurface below the apothecia.