Floral development in Aphandra (Arecaceae)

Abstract

The organogenesis of staminate flower clusters and flowers and some observations on the corresponding pistillate structures of Aphandra natalia are described and compared with those of the other two genera in the Phytelephantoideae (Arecaceae). In Aphandra, staminate flowers are borne in monopodial clusters of mostly four (1-6) flowers. Each flower is surrounded by two pairs of subopposite bracteoles and has two rather indistinctly four-parted whorls of perianth parts. Stamen primordia arise on a shallow apical dome and then centrifugally down the sides of a long, angled, and laterally flattened receptacle. Immediately before the staminate bud opens, the floral receptacle below the androecium rapidly elongates, becoming funnel-shaped, with the bracteoles and a perianth sheath adnate to it forming a pseudopedicel. Epidermal and subepidermal layers of these pseudopedicels split at anthesis and release a great number of raphide idioblasts that resemble the pollen grains in shape and size. It is hypothesized that the idioblasts deter pollen feeding or ovidepositing insects. The phylogenetic implications of these findings are important within the Phytelephantoideae and among palms in general.