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 (1,060 ft).

It has a leproid growth form, meaning that it looks like it is made of granules; the specific epithet refers to this characteristic.

Synarthonia leproidica contains psoromic acid, a secondary chemical that can be detected with thin-layer chromatography.