Floral development of Condylocarpon isthmicum (Apocynaceae)

Abstract

Apocynaceae is one of the largest families of angiosperms. Its representatives have flowers with relatively simple morphology, ranging from anthers free from the style head to more complex flowers in which the anthers are postgenitally united with the style head, forming a gynostegium, and those with a style head that is vertically differentiated into distinct functional regions. The aim of this study is to understand the morphology and secretory structures of Condylocarpon isthmicum (Vell.) A.DC. at different stages of development. This species, which is in the family Apocynaceae, has morphologically simple flowers. Flowers at four different stages of development were collected and processed for anatomical and histochemical analysis; floral anatomy was examined using light and scanning electron microscopy. The simplicity of the C. isthmicum flower morphology was contrasted with the complexity observed in the secretory structures at different stages of flower development. Four secretory structures were identified in this species: colleters, style head epidermal cells, nectariferous tissue, and an obturator. The colleters were observed in the bracts and bracteoles of the young inflorescences. The style head began the secretory phase in the pre-anthetic stage and remained in this phase until anthesis. The nectariferous tissue was secreted during anthesis, and the obturator was present only in post-anthetic flowers. We identified a nectary in the wall of the ovary, and we verified and described a new structure in the Apocynaceae, the obturator.