Porpidia soredizodes (Lamy ex. Nyl.) J. R. Laundon

    Thallus crustose, thin, more or less smooth, rimose to areolate, whitish, dull cream, pale brown-greyish, very pale grey-bluish, sometimes with orange or rusty sections on iron-enriched rocks, covered with egg-shaped soralia, 0.1-0.5 mm diam., more or less immersed in the thallus, scoured, granulose to farinose, containing pale greenish or pale greyish soredia. Apothecia rare and in limited number, 0.5-1 mm diam., disc black, exciple thick. Ascospores simple, ellipsoid, 15-20 x 6-9 µm. Photobiont: Chlorococcoid. Soredia : K+ yellow, Pd+ orange ; medulla I-, K/UV-. Rare, on rocks, notably slightly acid, like schists in old walls.

N.B. Very close to Porpidia tuberculosa and sometimes difficult to distinguish, but the soredia of the latter have negative chemical reactions (grey-bluish) and its medulla is I+ and K/UV+ purple. 

N.B. Porpidia soredizodes would be a sorediate morph of Porpidia crustulata and a complete range of intermediate specimen between these two species may be found.*