Taxonomy

Australian acacias, with a few exceptions, form a fairly distinct group within the whole acacia genus, and most of the Australian species are members of sub-genus Phyllodineae, with all but a few species of this sub-genus confined naturally to Australia. Some are widely cultivated, and even become weeds in other countries outside Australia.

Members of this sub-genus may in fact have more in common with other species in the mimosacea, (the family or tribe within the leguminosae where genus acacia is placed) than with the acacias of Africa and central America. An old name, Racosperma has been proposed by some botanists, and for this group to be classified as a separate genus in the mimosaceae. There is however no agreement on how or wether such a change in classification should happen.
There is some dispute over how to divide the whole acacia genus, wether into just two or more separate genus in the mimosaceae. Obviously it would be a quite mammoth task to change all the references let alone gain acceptance amongst the wider community, for such a well known widely regarded genus. Anyway, most Australian acacias may well be reclassified (renamed?) as members of a separate genus from acacia.
There is no definitive system for classifying these types or sections, though the sub-genus Phyllodineae is generally recognised as comprising different types or sections, and in fact not all species have phyllodes. These sections are based on generally easily recognisable differences in the flower, foliage and form. The sections generally recognised by most books or papers are the Juliflorae, Plurinerves, Phyllodineae, Pulchellae and Botrycephalae. Though the relationship between and specific members of these sections may be different. The Botrycephalae and Pulchellae are both sections with members having permanent bipinnate foliage, but are not necessarily related and in fact are confined to opposite sides of the continent, SE Aust and SW Aust respectively.
The smaller groups are generally only recognised in more technical papers, or in specific areas, the members of these sections mostly confined to a few areas of the north of the continent. There’s also a few extra Australian species from sub-genus Phyllodineae, and some species from sub-genus Acacia found in Australia, though they may have been introduced at some stage. A single species represents sub-genus Acueiliferum, in the far NE of the continent, other members of this sub-genus are found just to the north and through parts of SE Asia.
With possibly over 900 species or varieties of acacia in Australia it is obviously a complex task to try and relate all the species together. So these sections or groups simplify the process, and there are sometimes further sections or types within these. In some parts of the continent, SW WA more than 100 species of acacia can be found in a 1 x 1 1/2 degree (longitude x latitude) area, representing a very high diversity.
Even within the last 20-30 years quite a number of new species or varieties have been recognised, so it is quite literally a growing field!