We present a molecular phylogeny incorporating all five species of the Palaearctic geometrid genus Lythria, based on a 2810-bp combined data matrix comprising the full sequence of the mitochondrial gene cytochrome oxidase subunit one (COI) and fragments of the nuclear genes elongation factor 1 alpha (EF-1α) and wingless (wgl). L. venustata, which was recently rediscovered from Kazakhstan, is shown to be sister taxon to all other members of the genus. The remaining species within the genus form two pairs of sister species: L. purpuraria groups together with L. plumularia, and L. cruentaria with L. sanguinaria. The phylogeny is well supported by characters of the male genitalia of all Lythria species. In addition to the molecular phylogeny of the genus Lythria, we illustrate the external appearance of L. venustata for the first time and describe the anatomy of its male genitalia.