Description
Oxneriaria lichens form crust-like thalli that can vary from evenly cracked patches to rosettes with a radiating, wrinkled or lobed outer zone. In some species the surface is distinctly zoned, with the outer parts forming branch-like or tree-like aggregations. The thallus may produce powdery soredia or small bud-like isidia for asexual reproduction, though these are absent in some species. Beneath the main body there is usually a dark to black margin of fungal tissue ( hypothallus ), though this can sometimes be pale or missing. The outer cortex and algal layer are well developed, and the thallus attaches to the substrate through fungal filaments extending from the medulla. [1]
The fruiting bodies (apothecia) are of the aspicilioid or lecanorine type: at first immersed in the thallus, later becoming slightly raised and often clustered towards the centre. Their discs are typically flat or shallowly concave, sometimes dusted with a whitish coating ( pruina ). The apothecial wall ( true exciple ) is usually weakly developed. Inside, the spore-bearing layer contains simple paraphyses (supporting filaments) and asci that most often hold eight ascospores, though occasionally fewer. The ascospores are colourless, single-celled, and range from ellipsoid to nearly spherical in shape. [1]
Asexual spores (conidia) are also produced; they are slender and rod-shaped, straight or slightly curved. Chemical analysis shows that members of this genus characteristically contain substictic acid. The group differs from the related genus Aspicilia by its smaller spore size, the wrinkled or lobed margins of its thallus, and its occurrence mainly in polar and high-alpine regions, as well as its distinct position in the family Megasporaceae according to molecular phylogeny. [1]
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