Floral biology of two Vanilloideae (Orchidaceae) primarily adapted to pollination by euglossine bees

Vanilloideae comprises 15 genera distributed worldwide, among which are Vanilla and Epistephium (tribe Vanilleae). Based on field and laboratory investigations, the pollination biology of V.dubia and E.sclerophyllum was analysed. The former was surveyed in a semi-deciduous mesophytic forest at the biological reserve of Serra do Japi and in a marshy forest at the city of Pradopolis, southeastern Brazil. The latter was examined in rocky outcrop vegetation in the Chapada Diamantina, northeastern Brazil. In the studied populations, the tubular flowers of V.dubia and E.sclerophyllum were pollinated by bees. Pollen was deposited on either their scutellum (V.dubia) or scutum (E.sclerophyllum). The mentum region of V.dubia is dry, whereas that of E.sclerophyllum presents a small quantity of dilute nectar. Flowers of E.sclerophyllum are scentless, while those of V.dubia are odoriferous. Although V.dubia is self-compatible, it needs a pollinator to produce fruit. In contrast, E.sclerophyllum sets fruit through spontaneous self-pollination, but biotic pollination also occurs. Both species are primarily adapted to pollination by euglossine bees. Pollination by Euglossina seems to have occurred at least twice during the evolution of Vanilleae. Furthermore, shifts between rewarding and reward-free flowers and between autogamous and allogamous species have been reported among vanillas.