The genus was circumscribed in 2014 by lichenologists Sergey Kondratyuk, Ingvar Kärnefelt, John Alan Elix, Arne Thell, and Jae-Seoun Hur, following a molecular phylogenetics-led restructuring of the subfamily Caloplacoideae.

The genus name honours Norwegian lichenologist Eilif Dahl for his "important contributions to the Australian lichen flora".

The apothecia are biatorine in form and are encased in an outer layer, the true exciple, that is either paraplectenchymatous or scleroparaplectenchymatous.

In terms of chemical properties, the thallus does not change colour when exposed to the potassium hydroxide (K) spot test, but the apothecia turn purple.

Lichen products in the genus include the dominant presence of lichexanthone and anthraquinones linked to the parietin group (or chemosyndrome), with these compounds being most concentrated in the apothecia.