Rubiaceae include the greatest number of heterostylous species of any angiosperm family and this sexual system is likely to have evolved several times independently in the family. Variation in expression of heterostyly often has been attributed to incidences of independent evolution. Floral development was studied in three differently related heterostylous taxa in Rubiaceae with several goals. The first goal was to document how flowers of two different morphologies are produced by a single species. The second goal was to compare the developmental pathways leading to heterostylous flowers among species. The final goal was to determine if more closely related taxa have more similar patterns of development than taxa that are more distantly related. Ontogenetic data were collected from flowers in populations of Psychotria poeppigiana and P. chiapensis at La Selva Biological Station, Costa Rica, and from a population of Bouvardia ternifolia located in the Catalina Mountains near Tucson, Arizona. A series of buds representing different developmental stages were measured from plants of each species. Bud size, anther, style and stigma heights were recorded for each bud. Graphs plotted using these data contrast the ontogenetic trajectories of long-style and short-style flowers for both anthers and styles. Patterns of long-style and short-style floral development in both species of Psychotria are similar. Height differences between anthers of long-style and short-style flowers at anthesis appear to be due to unequal growth rates during development. Subtle differences in corolla development between floral morphs may contribute to inequality in anther height as well. Contrasts in style height appear to be set at very early stages in development as the result of a difference in distribution of tissue to the style versus the stigma between floral morphs.

Key words: Bouvardia, floral ontogeny, heterostyly, Psychotria, Rubiaceae