The Australasian dragonfly A. brevistyla is compared with its congeners, all geographically distant, and with spp. in other aeshnine and allied anactine genera. The results of these comparisons emphasise its taxonomic isolation, in particular from the South American spp. of Aeshna to which it had been thought to be allied. It appears to be more closely allied to the specialised Papuan and New Caledonian genus Oreaeschna, of which it may represent a forerunner. A new, monotypic subgenus of Aeshna. Adversaeschna, is described to receive it.