Preliminary Biogeographic Analysis of the Northern Territory Vascular Flora

Abstract

The Northern Territory vascular flora is composed of 190 families, 979 genera and 3411 species; 5.2% of the species are naturalised exotics. The native flora is equally dominated by Pan-tropic and Australasian genera (23%), followed by Old World Tropic (16%), Indomalaysian (14%) and Cosmopolitan (13%) genera. The northernmost and southernmost 5° latitude of the Northern Territory were cornpared. These environmental extremes have fewer taxa in large families and genera, and the northern section has many more families and genera with few taxa than the southern end of the Northern Territory. The majority of the genera from both extremes have tropical affinities. Analysis of three published schemes that subjectively regionalised the Northern Territory showed that all the schemes are imperfect, as some of the within-scheme regions were found to have statistically similar generic composition. Objective classification of the generic composition of 0.5 x 0.5° grid cells and the specific composition of 1.0 x 1.5° grid cells, based on Northern Territory herbarium records, produced largely coherent spatial groups with ecological reality.

Comparison of these two classifications with existing regionalisations revealed that Barlow's scheme best approximates them, although it is not detailed enough in the area north of 15°S. latitude and does separate the MacDonnell Ranges from the surrounding lowlands in central Australia. Comparison of the species classification with two objective regionalisations based on the recorded species distributions in two widespread genera (Acacia and Eucalyptus) revealed that the latter forms regions of a very general nature. One feature common to classifications based upon 1 : 250 000 map sheets is the floristic dichotomy at 17-18°S. The analyses presented here are preliminary because of the variable and incomplete collecting that has occurred throughout the Northern Territory. Accurate regionalisations can follow only after much more systematic fieldwork and collecting. This will be achieved by the current integrated Northern Territory vegetation mapping program.