[1] Up to four subspecies are listed by some authors, while others consider the willow beauty a monotypic species or accept only rhomboidaria and sublutearia as distinct:[2] Under its junior synonym Geometra rhomboidaria, the willow beauty is the type species of its genus Peribatodes.

The wings of this species are whitish-grey or -yellowish, though they have a buff or grey appearance from a distance, as they are heavily speckled with brown or black dots.

Running over the fore- and hindwings in a semicircle are the two blackish bands commonly found in Ennominae, but they are broken and somewhat indistinct in this species.

The adults are on the wing during summer – e.g. June to September on the British Isles, while in the more continental climate of Austria they are rarely seen anymore in late August.

[4] The caterpillar larva is reddish-brown and feeds on a variety of trees and shrubs, but – despite its name – rarely or never on willows (Salix).