Placynthium nigrum (Huds.) Gray
Lichen niger Huds., Fl. angl. 2: 524 (1778).
Thallus in rosettes, olive to blackish, to 3 cm diam., not effigurate, surrounded by a black, marginal prothallus. Lobes squamulose, flat, 0.4-1.5 mm wide, margins crenate or digitate, squamules scattered at thallus margin, crowded centrally, forming a continuous crust which may become areolate, areolae 1-4 mm wide and 1-3 mm tall. Isidia present or absent, cylindrical, 0.2-0.5 × 0.05-0.1 mm. Lower surface blue-green, rhizinate. Apothecia 1 mm diam., with dark proper margin, disc brown or black, concave at first becoming plane or convex. Ascospores narrow-ellipsoid, 1- to 3-septate, 7-18 × 3.5-7 µm.
S: Canterbury (Weka Pass, Flock Hill, Ashburton Gorge), Otago (Hampden), Southland (Clifden). On limestone.
Cosmopolitan
