Cladistic biogeography of plants in australia and new guinea: Congruent pattern reveals two endemic tropical tracks

Although congruence among multiple taxa is accepted as the basis of the cladistic approach to biogeography, seldom has congruence been tested for patterns within continents. Moreover, contiguous land areas are subject to confounding factors that might lead to incongruence, and areas of endemism are difficult to define. Most previous studies have analyzed single taxa and therefore could not test for congruence. Here, we report the first cladistic biogeographic analysis of multiple plant taxa (11 angiosperm groups) within continental Australasia. We have used Page’s (1994, Syst. Biol. 43:58-77) new mapping method implemented in his program COMPONENT 2.0, minimizing the optimality criterion “leaves added” which is the number of terminal branches that need to be added to reconcile all input cladograms with the general area cladogram. A randomization test showed significant congruence, and a jackknife test indicated which parts of the general area pattern are robust. Conflicting patterns shown by widespread species may have been influenced by recent range expansions. At least two independent histories are postulated for taxa endemic to the tropics. One appears as a close relationship between the monsoon tropical areas, including southern New Guinea, and the other is a track (a group of areas with a common history) of successive differentiation along the east and south coasts. The Australian wet tropics (the Atherton area), although geographically proximate to the monsoon tropics, are part of the east coast track. Tasmania shows a very early vicariance from the rest of the continent, and the central arid areas appear related to adjacent coastal areas rather than to each other (contra Cracraft, 1991, Aust. Syst. Bot. 4:211-227). The postulated exchange of taxa with southeast Asia following late Miocene contact was not tested because of a lack of suitable taxon cladograms. © 1995 Society of Systematic Biologists.