Floral biology of Passiflora urnifolia Rusby in the Yungas rain forest of Argentina

Abstract

Passiflora urnifolia is a poorly known species that is distributed in five countries in the centre of South America. In Argentina, it grows in the Northern rain forests. Its reproductive system, floral biology and pollinators remain unknown, so they were studied for the first time in the Argentine Yungas. Flowers open before dawn and close at dusk, displaying the three typical phases of the genus due to the style movement, being all pollen donors, while the second also functioning as pollen receptor. The concentrated nectar, present from anthesis, is replenished twice. Visual guides consist of concentric circles: white versus purple around the green centre in the visible, while reflecting versus absorbent in the UV spectra, respectively. The corona emits aroma, sweet and light. Among the diurnal flower visitors (5 species of hymenopterans, 2 of coleopterans, 2 of hummingbirds) and nocturnal (blatodeans and microlepidopterans), due to their activity on the flowers, contact with anthers and stigmas, abundance of pollen of P. urnifolia on body parts that contact the stigmas and the body dimensions that fit those of the flowers, the bees Xylocopa eximia, Bombus tucumanus and Apis mellifera can be considered pollinators. The floral traits indicate melittophily, in coincidence with the detected pollinators; though, the long pedicels that separate the flowers from the foliage and the slightly outward orientation of the anthers suggest that the hummingbirds could also pollinate. The high degree of self-pollination would compensate for the low frequency of pollinators in the mostly ever shaded lower stratum of the forest.