Floral ontogeny and anatomy reveal the gynophore origin and nature in <i>Bowdichia virgilioides</i> (Fabaceae)

Abstract A considerable number of papilionoid legumes have a basal stalk that supports the gynoecium in their flowers. We studied the ontogeny and morphoanatomy of Bowdichia virgilioides (Faboideae) flowers, aiming to investigate the nature and origin of this basal stalk. Flowers and floral buds were examined using scanning electron and light microscopy. This species exhibits acropetal floral initiation except in the carpel, which initiates synchronously with the first outer stamen. Sepal and stamen initiation is unidirectional from the abaxial side. No suppression or organ loss occurs in the primordium initiation. The curved hypanthium and decentralized gynophore result from the intercalary growth of the floral axis during the latter stages. The gynophore has a stem nature due to its eustele, from which one dorsal and two ventral bundles depart and irrigate the carpel. Due to its stem nature and receptacular origin, we conclude that the basal stalk of the gynoecium in B. virgilioides flowers is a gynophore sensu stricto. Putative floral secretory regions were identified, and an evolutionary discussion was presented. These studies are useful for the standardization of nomenclature for structures of similar morphology, nature, and origin and can also deepen our understanding of the gynoecium evolution in Fabaceae.