The Geonomeae are a neotropical palm tribe with six genera, Pholidostachys, Welfia, Calyptronoma, Calyptrogyne, Asterogyne and Geonoma, and up to 70 species. The morphological structure of the gynoecium in Geonomeae has been in general neglected. Todate, detailed studies on the reproductive structures have incorporated only two genera and less than 6% of the species within the tribe. A tri- or uniovulate gynoecium with slender, elongate styles has been traditionally considered as typical for the group. We have studied the flower morphology and anatomy of 15 species representing all genera of Geonomeae. The gynoecium of Geonoma shows three free carpels in early stages of development but later becomes pseudomonomerous. The other five genera show a more equally developed tricarpellate gynoecium, the two adaxial carpels being larger than the abaxial carpel. A central protrusion between the three carpels is present in some species of Pholidostachys, Calyptrogyne and Geonoma. The ovules in the tribe are attached at the base of the ovarial cavity or are pendent. They are more or less anatropous. In all Geonomeae a septal nectary is formed by the incomplete union of the flanks of the carpels at the base and mid-level of the gynoecium. Nectar is secreted from an epithelium, and non-secretory ducts are located at different levels of the ovary. Styles seem to emerge from the "base" of the ovary, because of the bulging of one of the carpels in pseudomonomerous gynoecia, but from the top in gynoecia with all three carpels equally developed. Protuberances in the dorsal walls of the styles were observed in Pholidostachys, Calyptrogyne and Asterogyne. The stigmas expose unicellular papillae at anthesis, in Welfia also multicellular papillae. Pollen tube transmitting tracts and a compitum are present in the ventral slits of the postgenitally united styles during anthesis.

Key words: Arecaceae, Geonomeae, gynoecium, morphology