Abstract
Floral visitors are often overlooked in those plants considered invasive and widespread weed species. Martynia annua L. is an example of an introduced species to the old world being native from tropical America, however, information of its endemic pollinators in the Neotropical region is missing. In this study, the floral visitors of M. annua were evaluated in Chamela Field Station (Chamela-Cuixmala Biosphere Reserve) in Jalisco, Mexico. Our aim was to provide information of the breeding system of M. annua and then indicate the potential pollinators. We included morphological and sexual features to estimate the outcrossing index (OCI). The frequency, behavior, and pollen loads were considered to find the potential pollinator. Despite the evidence of protandry and OCI indicating a xenogamous breeding system, the lack of herkogamy suggests M. annua is a facultative xenogamous species. The highest frequency of visits corresponded to the maximum diameter of corolla. Euglossa viridissima Friese was the most recurrent visitor. However, this species often carried a high proportion of heterospecific pollen and did not touch any sexual structure of the flower. In contrast, Centris agilis Smith performed as the most likely pollinator. Flowers of M. annua offer valuable rewards to its visitors and may be a good source of energy to those foragers capable of reaching the nectaries, though small bees are apparently unable to penetrate the flowers. We consider that there are evidence that suggests M. annua is a specialized melittophilic plant, pollinated by moderate to large-sized hairy bees throughout its distribution.