Resumen de Reproductive ecology of the globally invasive Whitetop Weed, Parthenium hysterophorus (Asteraceae)
B. Usharani, A.J. Solomon Raju
Parthenium hysterophorus L. is a weed of global significance, because of causing human and animal problems, agricultural losses, and threat to biodiversity. Particularly in this context, the information on its reproductive ecology is important so as to understand its reproductive traits that make this weed invasive at global level.
The study into its reproductive ecology indicates that it displays simultaneously vegetative, flowering and fruiting phases in different habitats, depending on the age of the plant and soil environment. The inflorescence is a heterogamous capitulum which begins anthesis with ray florets opening synchronously on the first day, while the disc florets open in the next five consecutive days. The ray florets are fertile, self-compatible, selfpollinating (vector mediated) and facultatively xenogamous, while the disc florets are female-sterile and act as pollen donors. In the disc florets, their tubate corolla, nectar secretion and echinate pollen are adaptations for entomophily, while the small spheroidal and powdery pollen form is an adaptation for anemophily. Butterflies, especially nymphalids and bees, are principal pollinators, while wasps and flies are supplementary pollinators.
Thrips, Frankliniella schultzei and Scirtothrips dorsalis, use flowers as breeding and feeding sites; the latter activity affects mostly self-pollination. Ray florets produce wedge-shaped cypselas crowned with persistent corolla appendages and stylar arms. Individual cypselas are liberated together with a straw-colored fruit layer and two adjacent lateral sterile disc florets, which collectively act as air sacs and aid the dispersal of cypselas.
