Description
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 ( areoles ) 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 prothallus ) can usually be seen edging the colony. The internal algal partner is a green chlorococcoid alga whose cells are frequently ellipsoidal; in many specimens the algal layer 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. [2]
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 discs are flat to shallowly cup-shaped and bordered by a wafer-thin rim of thallus tissue that seldom rises above the surface. The usual inner cup wall ( proper exciple ) 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 ( hypothecium ) 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 . [2]
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