The species epithet honors the Norwegian lichenologist Tor Tønsberg, who collected the type specimen from a deglaciated alluvial terrace in 2015.

[1] Lecidea toensbergii is a lichen characterized by its endolithic (within rock) hypothallus, which does not contain observable algae in the substrate and is unreactive to iodine-potassium iodide (IKI).

Its apothecia (fruiting bodies) are round, dispersed, and occasionally replicate by division, measuring 0.4–1.0 mm in width and 300–400 μm in height.

The lateral cortex is 30–60 μm thick, extending to the base of the apothecia, and the outer layer is brown or blackened, particularly in the holotype.

[1] The disc of the apothecia is round, reddish-brown, smooth, and epruinose (lacking a powdery coating), positioned lower than the thalline margin.