Phenakospermum guyannense is a monotypic, arborescent, long-lived monocot that is widespread in Amazonian South America. This outcrossing species is pollinated primarily by phyllostomid bats. Given these life-history characteristics,P. guyannense is expected to exhibit high levels of genetic variation and gene flow. We used isozyme electrophoresis and randomly amplified polymorphic DNA (RAPD) to characterize genetic variation in populations ofP. guyannense from French Guiana. Both measures detected a surprisingly low level of genetic variation, with only five out of twenty (25%) allozyme loci polymorphic (P), 1.35 alleles per locus (A), and an expected heterozygosity (He) of 0.090 at the species level. Isozymic genetic variation was even lower within populations (P = 17.5, A = 1.24, He = 0.074), and was corroborated by a RAPD assay that used 26 arbitrary primers (P = 3.61, A = 1.04, He = 0.014). Although overall levels of variation were low, the detectable variation was distributed as would be expected for an outcrossing species with extensive gene flow (mean GST = 0.230). We suspect thatP. guyannense is depauperate in genetic variation because of a series of bottlenecks that affected the species over this portion of its range.