A new chrysomeline genus, Ewanius, is described from Tasmania, Australia. The genus is founded on a single species, Ewanius nothofagi new species, a plesiomorphic member of the tribe Gonioctenini Motschulsky. Ewanius is compared with similar genera, particularly Araucanomela Bechyné and Bechyné and Novacastria Selman, and the classification of Chrysomelinae is briefly discussed. All three genera are monotypic and feed on Nothofagus.