The
thallus (lichen body) forms small
colonies to about 0.6 cm wide, usually outlined by pale brown lines where it meets neighbours (the ). It is whitish to pale olivaceous grey, continuous, thin (to roughly 0.1 mm in section), and partly sunk in the outer bark; the surface lacks a true (it is ) and appears and faintly . The is a green alga with
ellipsoid to roughly spherical () cells (about 7–14 × 5–8 μm).
Calcium oxalate crystals are scattered through the thallus.
Apothecia (
sexual fruiting bodies) are not known to occur in
G. mauritiae. Asexual structures are conspicuous but minute sporodochia (powdery pads that produce conidia) typically whitish, 0.1–0.2 mm across and up to about 0.05 mm tall, flat to weakly domed, and discrete to confluent. Conidia are produced from roughly 1.0–1.5 μm-wide
hyphae in tightly coiled chains constricted at the septa; individual conidia are 1-celled, irregularly
ellipsoid, usually curved, and typically about 3.1–5.0 × 1.5–2.5 μm, with thin
hyaline walls and a gelatinous coat bearing fine pale . Chemically, the species contains 2'-
O-methylperlatolic acid. Routine
spot tests on the thallus and sporodochia are K−, C−, KC−, Pd−; thallus hyphae are I− but KI+ (pale blue). The granular crystals in the sporodochia dissolve in K (
potassium hydroxide solution) with a clear solution and in
lactophenol cotton blue with precipitation of hyaline needles; they do not dissolve in
sulphuric acid. ==Habitat and distribution==