Floral development in Hura crepitans (Euphorbiaceae): a bat-pollinated species with multicarpellate gynoecium

Abstract

Hura crepitans L. stands out in the family Euphorbiaceae by being bat-pollinated, having inflorescences with a single female flower with a giant multicarpellate gynoecium at the base of a spike with a large number of male flowers. We described the structure and development of flowers of this species to understand the diversification of flowers in the family and how anatomical structures have adapted to bat pollination. Flower buds and flowers were fixed and embedded in paraffin and studied using scanning electron microscopy. Young male flowers are embedded in the axis of a spike. In both male and female flowers, the calyx is extremely reduced, the sepals united, in male flowers lacking vascularization. Petals are lacking. In male flowers, the androecium has 13–30 united stamens, arranged in (2)3(4) whorls. Female flowers have 11–14 uniovulate united carpels, each with a separate locule. The ovules are pachychalazal with vasculature in both integuments. The style is atro-vinaceous, forming a long column ending in a lobed stigmatic plate. Hura crepitans is similar to Algernonia and Ophthalmoblapton of Hippomaneae in the increased carpel number. However, flowers have some features that allow bat pollination, in contrast to the rest of the family which is more often insect- or wind-pollinated. Among these features are numerous stamen whorls with increased number of stamens, giant gynoecium, reduction in the perianth and a large stigma with central receptive surface.