Mecanismo floral e reprodução em Centrosema virginianum (L.) Benth

Abstract

The papilionaceous flowers are described in the literature as being flowers with secondary presentation of the brush type, where a series of trichomes on the stylet are responsible for the collection and deposition of pollen in the body of the pollinator for reproduction. The objective of the present study was to analyze the floral mechanism, ultraviolet reflection, pollen morphology, floral anthesis, frequency of visitors and breeding system of Centrosema virginianum, a papilionaceous species with flowers that has a purple and, less commonly, white coloration. For analysis of the floral mechanism, videos were recorded with simulations of visits to visualize the exposure of the floral structures and the pollen deposition, as well as to analyze the role of the brush in this mechanism of deposition. Tests of ultraviolet reflection with ammonium hydroxide were carried in purple and white flowers and analysis of pollen morphology through the acetolysis method. Floral buttons of purple and white flowers were collected for the accomplishment of the acetolysis and preparation of slides for analysis of the pollen morphology. For the floral anthesis, pre-anthesis buttons of purple and white flowers were observed until the beginning of the anthesis to record the time. 40 hours of observations were made to determine floral visitors and classify them as pollinators and plovers. For the breeding system, tests of cross-pollination and manual and spontaneous self-pollination, besides the control group (natural pollination) were performed. The brush mechanism consists of trichomes present from the tip of the stylet and has the function of sweeping the pollen from their anthers to the dorsal region of the insect and bringing the pollen from other flowers to be fertilized. The ultraviolet reflection tests showed that there are differences in the coloration of purple and white flowers, but there are no differences between the nectar guides of both, since they remain the same. The pollen grains of purple and white flowers differed only in size. The floral anthesis begins before 5:00 a.m. and lasts approximately thirteen hours. The main pollinators of C. virginianum are bees of the genus Bombus and Xylocopa, although bees of the genus Euglossa may be occasional pollinators, depending on the size of the flower. The flowers also receive visits of Lepidoptera of the family Hesperiidae, that are plunderers. None of the flower visitors distinguished between purple and white flowers. The species is self-compatible autogamous and, due to the low amount of fruits formed by spontaneous self-pollination, requires a vector to perform self-fertilization. Centrosema virginianum is a climber, herbaceous, autogamous species, but dependent of pollinators, although the flowers presents in purple and white colors, did not show reproductive and ecological differences between them.