Members of Rubiaceae have a variety of pollinator syndromes and the family includes more heterostylous species than any other angiosperm family. The incompatibility system and floral dimensions at anthesis were recorded for three differently related heterostylous taxa in Rubiaceae. It is hypothesized that patterns of the heterostylous syndrome will be most similar between more closely related taxa or, alternatively, between taxa that share similar pollinators. Data were collected from populations of hummingbird-pollinated Psychotria poeppigiana at La Selva Biological Station, Costa Rica and in Soberania National Park, Panama, and from hawkmoth-pollinated P. chiapensis also at La Selva. Hummingbird-pollinated Bouvardia ternifolia was studied in the Catalina and Santa Rita Mountains near Tucson, Arizona. Hand-pollinations of flowers in each species tested self, intramorph, and intermorph fertility. The incompatibility system was characterized by location of cessation in pollen tube growth. In all three species, cessation of incompatible pollen tubes appeared to be different between long-style and short-style flowers. In short-style flowers, the incompatibility reaction typically occurred at the stigmatic surface. In long-style flowers of P. poeppigiana the incompatibility reaction most often occurred in the style. In long-style flowers of Psychotria chiapensis and Bouvardia ternifolia the incompatibility reaction occurred either in the stigma or style. Flowers of all three species have significant differences in stigma and anther heights at anthesis corresponding to long-style and short-style flowers. However, stigma and anther heights of long-style and short-style flowers are not reciprocal. Anther heights form a near continuum from long-style to short-style flowers in each species. Stigmas of long-style and short-style flowers from both populations of P. poeppigiana fall into two distinct height categories. Stigma heights of floral morphs overlap in some plants of Bouvardia ternifolia in both populations studied and in P. chiapensis.

Key words: Bouvardia, floral morphology, heterostyly, incompatibility system, Psychotria, Rubiaceae