Peltigera didactyla (With.) J. R. Laundon

    Thallus foliose, often limited (notably at first) to a few ear-shaped lobes, more or less immersed in the ground, sometimes, when mature, forming rosettes, 3-5 cmm diam., margin upturned, finely tomentose; upper surface grey, grey-brownish, brownish to green olive, young specimen more or less covered with laminal soralia, greyish, dull grey-yellowish, soralia vanishing at maturity with apothecia development; lower surface whitish, prominent veins, rhizine simple, brownish, seldom brush-shaped. Apothecia located towards lobe margins, isolated or in small clusters (2-4), erect and finger-shaped in old specimen, exciple indented or crenulate, brown-reddish then brown-chesnut. Ascopores narrowly elongate, acicular, 3-7-septate, 40-75 x 3,5-4,5 µm. Photobionte : Nostoc. Thallus and soralia chemical spot tests negative. Typical of wastelands and badlands, paths and tracks shoulders, waste heaps and quarries, etc. This species is polyphyletic and encompasses several taxa including Peltigera extenuata (Vain.) Lojka of which the soralia are C+ red, KC+ red. When adult, and devoid of soralia, easily mistaken with Peltigera rufescens and  Peltigera membranacea that may be found in the same habitat.