Leucodecton forms a thin,
crust-like
thallus that lies flat on the bark or rock surface. Its upper layer is usually cream to pale
fawn; the outer "skin" () is only weakly developed, giving the surface a smooth to slightly knobbly look. Large, irregular crystals may be embedded in the interior, but the border () that some lichens display is missing. Vegetative
propagules used for
asexual spread—powdery
soredia or tiny finger-like
isidia—occasionally occur. The
photosynthetic partner is a filamentous
green alga from the genus
Trentepohlia, which lends an orange tint when exposed in damaged areas. The reproductive bodies are flask- to urn-shaped
apothecia that start out immersed in the thallus and often push up in small wart-like clusters. Their black are usually concave, sometimes dusted with a grey bloom (), and are framed by a rim of thallus tissue () that may split irregularly as the fruiting body matures. Beneath this rim lies a —an internal ring of densely intertwined fungal
hyphae—seen in a view from above. Within the apothecium, the colourless
hymenium houses slender
asci, each with a single functional wall layer that thickens abruptly at the tip. The asci typically hold one to eight
ascospores. Spores are elongated to spindle-shaped, with several internal walls; they begin colourless and thin-walled but often darken and develop thick, laminated walls as they age. No
conidiomata (structures that produce
asexual spores) have been observed. Chemically, most species produce
stictic or
norstictic acid,
secondary metabolites that are useful for species identification through
thin-layer chromatography. ==Species==