Pollination mechanisms in Passiflora species: The common and the rare flowers- ecological aspects and implications for horticulture

Abstract

Passionvines have flowers with the following basic architecture: 5 sepals, 5 petals, a corona formed by concentric cycles (radii, pali, operculum, limen) and an androgynophore that bears 5 anthers, the ovary, 3 styles and 3 stigmas. Self-pollination may be achieved but some species are self-incompatible, so pollen vectors are required. The different relative sizes and orientation of the floral pieces of the various Passiflora species have implications on which visitors will pollinate; to perform pollination, they must have the adequate size to contact both anthers and stigmas in the same or in successive visits to different flowers. Pollen removal (from the anthers) and deposition (in the stigmas) is carried out by means of different parts of the body of the different pollinators, depending on their size and behaviour. The anthers are dehiscent and the stigmas are receptive as soon as the flower opens until it closes. The styles move throughout anthesis: they tilt down to the anthers and uplift afterwards. Thus, three floral stages occur: in the first and the third, only the anthers can be contacted by the legitimate visitors while in the second, both the anthers and the stigmas are placed in the way of the pollinators. The style movements succeed in all the studied species. However, in some species, in a proportion of the flowers the styles remain upright since the flowers open. These flowers are not able to receive pollen, neither by the pollinators nor by themselves, so they are functionally staminate. In fewer species, the dehiscence of the anthers does not happen in some flowers, so they are functionally pistillate. Finally, the three types of flowers may coexist in the same plant. This brings about the simultaneous occurrence of pollen donor-receptor flowers and only pollen donors, pollen donor-receptor and only receptor flowers or the three types of flowers in a single plant, respectively, leading to the corresponding functionally andromonoecious, gynomonoecious or trimonoecious systems. Certain floral traits seem to be associated with the absence of styles movements, such as a less developed gynoecium, minor-sized and nectarless flowers. In this chapter, an update of the recorded aspects at the moment as well as original data are discussed, taking in account the ecological interpretations of style movements, analysing the possible causes of the incidence of the less frequent flowers and considering the implications for fruit production in this edible fruited genus, some species of which are grown commercially.