Umbilicaria maculata

The thallus of Umbilicaria maculata is monophyllous, meaning that it consists of a single more or less orbicular, flattened, leafy lobe with a single point of attachment to the substrate. It is grey to grey–brown in colour with some whiter regions, and up to 3 cm (1.2 in) in diameter with a smooth, dull upper surface. The thallus undersurface is also smooth and dull, with a pale creamy to white colour that darkens towards the edges. The medulla is white and comprises two layers: a loose upper part with a webby (arachnoidal) plectenchyma, and a more compact plectenchyma in the lower part.^[1]

Apothecia (spore-bearing structures) are black and about 1 mm in diameter; they have an apothecial disc with central column of sterile tissue (omphalodisc) and a fissure in the centre. The asci are club-shaped (clavate), contain eight spores, and measure 40–45 by 10–15 μm. Ascospores are hyaline and with dimensions of 10–12 by 5–6 μm.^[1]

Umbilicaria maculata grows on the vertical faces of siliceous rocks in alpine and subnival habitats, preferring locations that are shaded and exposed to wind. Originally known from only a few location in the Tatra Mountains,^[1] it has since been reported from Uvernet-Fours in southeastern France, where it was found on the vertical faces of large blocks of Annot sandstone, at an elevation of 2,324 m (7,625 ft). The authors call the lichen "extremely rare", but acknowledge that its true distribution is not well understood because of potential confusion with the lookalike Umbilicaria cylindrica.^[2]