A new system for determining which plant species are indigenous in Australia

Abstract

An examination of Floras and related literature from various countries of the world has revealed a wide range of interpretations and concepts for indigenous plants. Nevertheless, an indigenous plant species has been universally defined as one that was not deliberately or accidentally introduced by man. An important recent addendum to the ‘indigenous’ definition is that it must disperse from an area where it is considered native. Particularly problematic are the so-called ‘pantropical’ or ‘cosmopolitan’ plants. These species are usually invasive and abundant, but most could not have crossed major barriers without the assistance of humans, and hence should be regarded as non-native species throughout much of their range. The accurate assessment of the alien or indigenous status of these and other taxa has been hampered by a lack of knowledge about their geographic origins and dispersal ability. Australian botanists have frequently adhered to a concept of indigenous plants being any that were thought to be present before European settlement in their region of interest – 1788 for the Sydney area, and as late as the 1850s for northern Australia. This definition is unrealistic and unworkable, especially when considering the ‘pantropical’ species. The transport of plants by maritime traders and explorers into the Indonesian and west Pacific areas has occurred for at least the past 3000 years. European colonisation in those areas from the 16th century accelerated plant introductions. Some of those plant species undoubtedly made their way to Australia before European settlement. This paper presents explicit definitions for indigenous (native) or alien (exotic, introduced, non-indigenous) plant species in Australia. A system of assessment using a combination of ecological, phytogeographical and historical criteria (the EPH system) allows the determination of ‘origin status’ for individual species. As a case study, data are presented for 40 plant species of disputed origin status. These species are assessed against the criteria, and a recommended origin status given for Australian occurrences.