Peltigera aphthosa (L.) Willd.

       Foliose thallus formed of large concave lobes 1-3 cm wide and 5-8 cm  long  with a rounded, sinuous margin that is straightened to form a small cup,  arranged in rosettes 15-25 cm in diameter. Upper surface smooth, grayish slightly greenish when dry, bright shiny green when wet, covered with warty cephalodia with Nostoc, of 1-2 mm scattered over the entire surface, grayih-blackish; lower surface not or very little veined, whitish and tomentose towards the margin, grayish-black to black in the center with fasciculated rhizines. Apothecia very rare, terminal, saddle-shaped, brown. Ascospores hyaline, acicular, 3-7 times septate, 50-70- x 4-5 µm. Photobiont: chlorococcoid. K-, C-, KC-, P-, UV-, (medulla sometimes K+ pink, KC+ pink, fleeting). A mountain, subarctic, and boreal species that grows on the mossy ground of forests.

N.B. A vicariant species of Peltigera leucophlebia which is less mountainous and whose underside is very veined.