Bellemerea species form firmly attached, crust-like colonies on hard, often
siliceous rock. Seen close up, the surface is broken into angular blocks or low warts () that may be scattered or jammed tightly together.
Thallus colour ranges from chalk-white through pale grey to
ochre or even rusty brown, and a thin black "seam" of
hyphae (the ) can usually be seen edging the colony. The internal algal partner is a green alga whose cells are frequently
ellipsoidal; in many specimens the runs unbroken beneath the fruiting bodies. When a drop of iodine is applied, the inner white layer (
medulla) turns a deep violet—an easy field test for the genus. The
sexual structures are small black discs (
apothecia) that start buried in the areoles but often expand until they fill almost the whole surface of a single block. The are flat to shallowly cup-shaped and bordered by a wafer-thin that seldom rises above the surface. The usual inner cup wall () is extremely thin or missing altogether, so the disc appears to pass straight into the surrounding crust. Under the microscope the spore layer (
hymenium) is threaded by branched, cross-linked
paraphyses whose tips swell slightly and carry a faint brown cap; the layer below () is colourless. Each club-shaped
ascus contains eight smooth, colourless
ascospores that are single-celled but sometimes show a faint ghost
septum; a distinctive iodine-positive inner wall and a clear gelatinous envelope surround each spore. Minute, sunken
pycnidia release short, rod-shaped
conidia for
asexual spread, and
thin-layer chromatography detects
norstictic acid in several members of the genus. The combination of spores with an iodine-blue perispore, colourless cup wall and colourless hypothecium distinguishes
Bellemerea from superficially similar crustose genera such as
Amygdalaria,
Aspicilia and
Porpidia. ==Species==