[4] Physcia magnussonii has a heteromerous and dorsiventral thallus with narrow lobes that form tightly packed, circular rosettes.

The underside of the thallus is white to brownish, featuring a few thick and simple rhizines, which are root-like structures that help anchor the lichen.

[1] The spores are one-septate (divided into two cells by an internal partition, or septum), brown, and narrowly ellipsoid, measuring 16–24 by 6–9 μm.

They have a unique verrucose (warty) ornamentation and have thickened walls at the apex and septum, typical of the genus Physcia.

[1] Variolaric acid is a secondary metabolite (lichen product) that has been shown to occur in some Norwegian specimens of Physcia magnussonii.

[5] Zwackhiomyces turcicus is a lichenicolous fungus that was reported growing on the thalli of Physcia magnussonii lichens in southern Turkey.