Members of the genus Thelotrema are commonly called barnacle lichens.

[3][4] Thelotrema lichens have a thallus with colours ranging from white to yellow-grey or light olive.

The texture of the thallus can be smooth, uneven, or verrucose, with the presence of either an ecorticate surface or a loosely to rarely dense proso- to paraplectenchymatous cortex.

The photobiont layer and medulla frequently contain clusters of calcium oxalate crystals.

[5] Thelotrema ascospores are transversely septate to muriform, fusiform-ellipsoid to oblong-cylindrical, and feature thin to thick septa with angular to rounded lumina.