XVI International Botanical Congess

The recent collection of ca. 4000 plant specimens from the 360,000 ha Iwokrama Reserve in central Guyana affords an opportunity to study the floristic diversity of this poorly known region. Intensive collecting throughout the region was carried out to produce a checklist of the reserve's flora. The checklist, numbering 1000 spp., was compared with checklists of areas of comparable size in Guyana (Kaieteur Falls, Guiana Highland, Mabura Hill, low elevation forest, northern Guyana), French Guiana (Central French Guiana, low elevation forest, Guiana Shield), and the Biological Diversity of Forest Fragments Project, Manaus, Brazil, representing northern South America apart from the Guiana Shield, to discern the extent to which Hylaean, Guiana Highland, and Guiana Lowland elements contribute to this flora. The results indicate: 1) Guiana Highland elements are represented at low elevation on sand substrates. 2) An endemic Guiana Lowland element is represented on granite-derived soils. And 3) A relatively small fraction of the flora is represented by widespread, Hylaean elements.