 It is one of two subregions of the Mallee region, the other being Eastern Mallee.The Mallee, Avon Wheatbelt and Geraldton Sandplains regions together comprise Hopper's Transitional Rainfall Zone of Beard's South West Botanical Province.Under the World Wide Fund for Nature's regionalisation of the world's terrestrial surface into "ecoregions", the Western Mallee subregion falls within the Esperance Mallee ecoregion, one of 6 ecoregions comprising the Southwest Australia ecozone.