Reproductive Biology and Pollination of the Parasitic Plant Psittacanthus Calyculatus (loranthaceae) in Central México1

Abstract

Psittacanthus is the only genus in the family Loranthaceae that is considered a significant pest of woodlands and farmlands in Mexico and Central America, but relatively little attention has been given to the reproductive biology and pollination of natural populations. We present quantitative information on the floral morphology, breeding system, flowering phenology, nectar production, floral visitors, and pollinators of the mistletoe Psittacanthus calyculatus in Tlaxcala, México. Its flowering phenology extends from April to October, with a major peak in July. Flowers last 5 days and produce abundant nectar (2.34 ± 0.175 µl per flower) with a constant sugar concentration (ca. 22%) throughout flower life span. Hand self-pollinations showed that this species is partially self-compatible (44% fruit set), whereas emasculated flowers produced no seeds. Hand out-crossed flowers produced a similar number of fruits (96%) compared to unmanipulated control flowers visited by birds and insects (84%), showing no evidence for pollen limitation. Four hummingbird species were frequent visitors of mistletoe flowers, but they varied in visit duration and number of probes per flower. Artificial pollination of flowers with stuffed hummingbirds of the four species suggested that Hylocharis leucotis was the most effective pollinator.