Synarthonia leproidica

Synarthonia leproidica is a species of saxicolous (rock-dwelling) and crustose lichen in the order Arthoniales. Found in Luxembourg, it was formally described as a new species in 2020 by lichenologists Damien Ertz, André Aptroot, and Paul Diederich. The type specimen was collected in the Vallée du Lellgerbaach (Lellingen) at an elevation of 323 m. Here the lichen was found on a siliceous wall at the edge of a forest path in an oak-hornbeam forest. It has a pale greyish crust-like thallus with dark brown/violet tinges. It has a leproid growth form, meaning that it looks like it is made of granules; the specific epithet refers to this characteristic. The thallus forms patches that are about 0.5–5 mm in diameter, although neighbouring patches can coalesce to form larger patches up to 10 cm in diameter. Synarthonia leproidica contains psoromic acid, a secondary chemical that can be detected with thin-layer chromatography.