Information on pollination ecology is essential to understand the sexual reproduction in Bidens pilosa L. The study is aimed at providing details of sexual system, breeding system, pollination mechanism, pollinators, seed dispersal modes and germination aspects B. pilosa based mostly on field study. Paper chromatography technique was used for recording sugar and amino acid types in the nectar since they are important to evaluate the pollination syndrome. The study indicates that B. pilosa displays vegetative, flowering and fruiting phases throughout the year. The plant produces heterogamous capitula with all ray florets opening on the first day and disc florets opening on the next four consecutive days. The ray florets are sterile while disc florets are fertile, dichogamous, protandrous, herkogamous, self-compatible, self-pollinating (vector-mediated) and facultative xenogamous. The disc florets display secondary pollen presentation. The tubate corolla, production of sucrose-rich nectar with essential and non-essential amino acids, and tri-colporate, echinate tri-colpate pollen grains in disc florets suggest entomophily. The plant is accordingly entomophilous but principally psychophilous. Disc florets produce non-dormant, long and short cypselas from the same capitulum. Seed dispersal is polychorous involving anemochory, anthropochory, zoochory and ombrohydrochory. The long cypselas of disperse farther away from parental sites and germinate readily under a wide range of conditions while short cypselas disperse to short distances and germinate under specific germination conditions at parental sites/in similar habitats. Therefore, the plant with secondary pollen presentation, facultative xenogamy, insects as pollinators, bimorphic cypselas and polychory is able to grow as a widespread weed.