The genus was circumscribed in 2008 by Sanja Savić and Leif Tibell, with Atla alpina assigned as the type species.

[3][4] Atla lichens have crustose thalli that are blackish in colour with a surface texture ranging from warty (verrucose) to diffusely areolate to immersed in the substrate.

Ascospores are ellipsoid, hyaline to dark brown when mature, and measure 43–87 by 19–49 μm; the spores are muriform (divided into compartments), with 7–15 transverse and 2–5 longitudinal walls.

The excipulum (the ring-shaped layer surrounding the hymenium) is spherical, ranging in colour from black to dark brown.

The involucrellum (the upper, often exposed covering or cap external to the excipulum) is well developed; depending on the species, the upper part of this structure is either fused together with the excipulum, or missing altogether.