Abstract
The evolution of the flora of the Amazon lowland is closely interconnected with that of the
Guayana highland. It is argued that the major upheaval of the Roraima sandstone formation, which
forms the Guayana highland, is a more recent phenomenon than generally accepted and has lasted
until the Neogene or even the Pleistocene. It is hypothesized that the main differentiation of a
psammophilous lowland flora, implying an ample symbiontic relationship with ectotrophic mycorrhyza,
has taken place on the sandstone plate of the Roraima formation previous to its upheaval in the Upper
Cretaceous and Neogene. With the upheaval, most elements of this specialized flora were left behind in
the warm lowland on white sand habitats peripherical to the inselberg mountains and the highland as
a whole. For the major part, these sand masses were derived r¡om the erosion of the Roraima massif.
On the highland itself, and probably concomitantly with the upheaval, a largely endemic flora evolved
on the basis of immigrations mainly from the Andes, but from the Central Brazilian Shield as well. In
the present lowland flora of Amazonia, a major dichotomy separates the ectotrophic psammophilous
flora on white sand from the anectotrophic forest flora on latosols.
