A presumed case of functional convergence between the flowers of Schizolobium parahyba (Fabaceae) and species of Malpighiaceae

Abstract

Flowers of Malpighiaceae have a flag petal with a sturdy base that Centridini bees clasp with their mandibles to free their legs and thus be able to harvest oil. We found that the yellow, nectariferous flowers of Schizolobium parahyba (Fabaceae) have a forward-flexed upper petal with a sturdy claw and an adnate filament. Two Centris species were among the most frequent bee visitors to S. parahyba flowers. These bees clasped the adnate filament and the claw of the upper petal with their mandibles and extended their mouthparts into the corolla to take nectar. During the visit they leaned on, or loosely grabbed, the stamens. Blooming in the same area and period were two yellow-flowered Stigmaphyllon species (Malpighiaceae) whose pollen was also found on loads carried by the Centris bees. The flexion and the sturdiness of the upper petal claw of Schizolobium parahyba flowers may be viewed as a trait that suits the mandible clasp of Centris bees. Although this clasp is not needed when the bees visit S. parahyba flowers, it is vital when the bees exploit flowers of the Malpighiaceae. We suggest that the sturdy claw and the adnate filament of S. parahyba may be viewed as an instance of presumed functional convergence with the upper petal of Malpighiaceae.