Floral function in relation to floral structure in two Periploca species (Periplocoideae) Apocynaceae

Abstract

This study comprises an investigation into the floral function in relation to the floral structure of Periploca aphylla and P. angustifolia, using light and scanning electron microscopy. Both species display the following floral structures: style-head bearing pollen translators, shelf-like nectaries, staminal feet, nectar-collecting troughs, trisegmented corolline corona lobes and corolla lobes, and anthers and nectaries covered by unicellular hairs. Lateral segments of adjacent corona lobes are fused with half of the adaxial base of the adjacent corolla lobes, creating openings through which pollinators can reach the nectar-collecting troughs in the corolla base. Flowers are rotate with spreading corolla lobes and exposed gynostegium, thus sorting in the open-access fly pollination system. The following features are useful to distinguish the flowers of the two species: corolla color, presence or absence of long unicellular hairs and white spots size on the adaxial surface of corolla lobes, translator length, pollen tetrads color, and presence or absence of linear tetrads. It seems that the floral modifications of the two Periploca species serve to optimize pollination efficiency by attracting a wide number of pollinators, thus enhancing the pollination success of plants.