Rhizocarpon lavatum (Fr.) Hazsl.
Thallus crustose, to 10-12 cm across, smooth to slightly rimose, cracked, areolate, areoles angular, 0.5-1 mm diam., pale grey tinged with ochre-yellowish or reddish, sometimes in shade ochre-greenish and even entirely greenish, prothallus absent except in case of contact with other crustose lichens. Apothecia usually numerous, immersed in the thallus and little protruding, 1-1.5 mm diam., disc flat or sometimes umbonate towards the center, blackish, exciple thick, persistent, paler, sometimes more or less skewed. Ascospores colourless at first then light brown at maturity and brown when old, muriform, 30-40 x 14-18 µm. Photobiont: Chlorococcoid. Chemical spot tests negative. Rather rare, on siliceous rocks periodically imersed on rivers and streams banks, sometimes on very humid or seeping rocks of cliffs. Often together with Ionaspis lacustris or Ionaspis ceracea. See Aspicilia laevata of which the thallus is smooth, brighter and more green-bluish, Pd+ orange and with simple ascospores.*