Thallus greenish yellow, spreading more or less radially, and reaching up to 10 cm; forming discontinuous patches, and appearing like small warts grouped together. Across section the cortex is up to 35 µm thick, with a thinner hyaline layer on top, but the lower part densely interspersed with crystals. Photobiont, located in a layer below the cortex, consists of chlorococcoid algae, 10-15 µm diam, possibly a species of Trebouxia. Anamorph: Pycnidial, black 50-100 µm diam, but usually forming irregular clusters up to 0.25 mm wide, which open by a longitudinal slit. Pycnidial wall consisting of thick walled isodiametric cells, never surpassing 5 µm in diam. Conidiogenous cells hyaline and ampulliform producing aseptate and colourless conidia which can be bacilliform to narrowly ellipsoidal, ca 4 x 1.5-2 µm. Teleomorph: Ascomata non pruinose apothecia, mostly 200-350 µm wide, black, and immersed in thallus warts which can be up to a millimetre across, and appear ‘lecanorine’. Exciple black and thin throughout, even at the base, up to 35 µm wide, formed by dark, thick-walled, and interwoven hyphae. Hypothecium very thin, unpigmented. Asci clavate at first, but becoming obpyriform and soon evanescent, 15- 20 (-27) x 4-7 (-10) µm, octospored. Ascospores dispersed passively and synchronously (a mazaedium), and continue to mature once the ascus dissolves to become sub-muriform, (13-) 20-30 (-33) x (11-) 14-20 µm, broadly ellipsoidal, brown, with smooth, thick walls; the number of septa in the ascospores vary from one to seven, and septum formation starts with 1- transversal division, followed by longitudinal and/or oblique ones. Chemistry: The thallus contains rhizocarpic acid, which is a tetronic/pulvinic acid derivative, but this cannot be detected by spot tests using K, C, KC or Pd, only by chromatography. This acid provides the distinctive greenish yellow colour of the lichen.