The ability of phylogenetic water stress and `shared-pollinator\ hypotheses to explain flowering times was tested for the flora of Barro Colorado Island Panama. Both quantitative (217 species) and qualitative (1173 species) flowering data were used. 2 Descriptive metrics calculated from quantitative flowering data indicated that mean flowering times fell in the final two months of the dry season and the first two months of the wet season for 56% of species and that flowering was concentrated in a short predictable part of the year for the great majority of species. 3 The `shared-pollinator\ hypothesis predicted that congeners should have temporally segregated flowering times. This hypothesis was rejected for 57 of 59 genera. 4 The water stress hypothesis predicted that species from drier habitats and life forms with limited access to soil water should flower in the wet season. This hypothesis was also rejected. 5 There were however strong phylogenetic patterns. Both the mean and the variance of flowering times were similar among congeners. The variance of flowering times was also similar among confamilials and mean flowering times were concentrated in the wet season for monocotyledons.