The species of an ill-defined assemblage centred around Aphalara exilis are revised. Two species, viz. A. siamensis and A. taiwanensis, are described as new and three species are synonymised (A. soosi with A. exilis, A. kunashirensis with A. itadori, and A. augusta with A. fasciata). A neotype is designated for Tettigonia exilis, a lectotype is designated for Aphalara rumicis Mally, and Aphalara ulicis is removed from synonymy with Aphalara calthae. The species are diagnosed, illustrated and keyed. The revision of types of A. polygoni, the type species of Aphalara, showed that it had been misinterpreted and that it corresponds to A. rumicicola Klimaszewski which is synonymised with it. A. polygoni auct. nec Foerster is described as A. freji sp. n. A list is given of the 37 currently recognised valid species of Aphalara with their distributions and host plants, and of 4 nomina dubia. A cladistic analysis using PAUP yielded 5 most parsimonious trees suggesting that Aphalara contains six monophyletic species groups (the itadori (2 spp.), siamensis (1 sp.), exilis (7 spp.), rumicis (2 spp.), maculipennis (4 spp.) and calthae (21 spp.) groups). Biogeographical aspects are analysed in terms of area relationships (BPA), ancestral areas (methods of Bremer and Ronquist) and dispersal (cladistic subordinateness). Four species groups are restricted to the palaearctic, one to the nearctic and only one occurs in both. It is concluded that vicariance events may have occurred in the palaearctic but that the presence in the nearctic is probably due to dispersal. The east palaearctic is likely to have been part of the ancestral area of Aphalara. Three of the species groups are monophagous on Polygonum, two on Rumex and one is polyphagous on Polygonaceae (Polygonum, Rumex), Brassicaceae, Caryophyllaceae, Primulaceae and Ranunculaceae. Polygonum is the likely ancestral host association of Aphalara; Rumex has been colonised independently at least three times.