ABSTRACT
The biogeography of the neotropical flora since the last glacial maximum is poorly understood. In this study, two biomes, the Chacoan and the Paranean, were investigated. Three homogenous communities are identified: the chaco seco, the chaco seco with a psammophilous facies (generally characteristic of sandy soils) and the Paranean semideciduous forests. Three ecotonal communities are also defined: the chaco húmedo, the Paranean ecotone intermingled with chaco elements, and the Paranean ecotone with cerrado elements. In order to describe the affinities of these communities with other South American vegetation types, we describe three distribution patterns and gradients between the Chacoan pole, the Colombian pole and the Paranean pole. Integrating Mueller’s concept of dispersal centres in a model based on the distribution patterns of selected tree species, we can discuss several hypotheses of floristic history, and especially the proposition that present-day Paranean forest is a remnant of a residual Pleistocenic seasonally dry forest flora.
