Flower Structure and Reproductive Biology in <i>Aspidosperma quebracho‐blanco</i> (Apocynaceae), a Tree Pollinated by Deceit

Abstract

Flower structure, attractants, breeding system, and visitors were studied in Aspidosperma quebracho-blanco, a South American mass-flowering tree with simple moth-pollinated flowers and without floral reward. Flowers are protandrous, having an initial male phase for 2 d. The pendulous and horizontal flower position and protandry prevent self-pollination. Although an inconspicuous annular floral nectary is located at the ovary base, nectar is not secreted. Nonstructural, extrafloral nectaries have been found on the external surface of the calyx and corolla, the first report of the kind for the family. Ants, wasps, flies, and beetles collect the extrafloral exudate composed of fructose, glucose, and sucrose. Experiments indicate that natural selfing (autogamy) and agamospermy are unlikely to occur (0% success), but artificial selfing indicates self-compatibility (70% success). A very low natural fruit to flower ratio (0.03) was obtained. Floral features and nocturnal opening indicate that these flowers would be pollinated by moths that nocturnally visit the species (Noctuidae, Pyraloidea) finding no floral reward. We suggest a nonmodel deception mechanism: providing the same cues as most moth flowers, this tree seems to be dependent upon sympatric rewarding plants that share the same pollinators.