The native flora of southern Australia has links with that of the other southern continents, reflecting their common origins in the Gondwanaland palaeoflora (Nelson, 1981). It also has later links with the floras of the landmasses to the north of Australia which developed after the Australian plate drifted northwards and collided with the Pacific plate to the north-east and the Eurasian plate to the north-west (Powell, Johnson & Veevers, 1981). As a result of these influences the areas of mediterranean climate in southern Australia developed a flora physiognomically similar to, but genetically distinct from, that of other areas of mediterranean-type climate (Raven, 1973).

Southern Australia, however, now shares many species with other mediterranean areas of the world. This sharing has been a dual process. One aspect of the process is slow and largely confined to a particular environment, whereas the other has been rapid and affects all environments. The first process is the acquisition of species as a result of bird migration between wetlands and surrounding areas of the northern hemisphere and similar environments in the southern hemisphere (Kloot, 1984). The propagules may adhere to migrating birds (and other creatures) or they may be small seeds caught in mud which escaped preening. Whilst this transportation is both rare and erratic it has been going on annually for some 70 million years. The large number of birds involved each year over such a long period ensured that even extremely rare events could have occurred a number of times.