Pollination biology of Callistemon citrinus (Curtis) Skeels (Myrtaceae)

Abstract

The pollination biology of Callistemon citrinus (Curtis) Skeels, popularly known as bottle brush tree (Myrtaceae), a highly ornamental tree was investigated. In Calicut, it flowers throughout the year, except in July with peak blooming in April-May. During the peak flowering period, nearly 150±50 flowers/plant bloom every day. Inflorescence is a pendent spike with flowers opening between 1100 and 1200 h in an acropetal succession and the life span of an individual flower is 3-4 days. Anthers dehisce between 1300 and 1400 h. Fresh Pollen grains at the time of anthesis showed maximum (94.2±2 %) viability, thereafter the viability decreased steadily. Nectar is secreted on inner hypanthial disc atop the ovary. Flowers are visited by several birds, wasps, bees, butterflies and ants. Among these Nectarinia zeylonica, Loriculus vernalis, Chloropsis jerdoni, Vespa affinis, Polistes spp., Apis dorsata and Apis cerana are major pollinators. Other floral visitors include Trigona irridepennis, Tetragonula sp., various ants like Anoplolepis gracilipes, Camponotus parius, Polyrachis sp., butterflies like Euploea core, Rapala manae and Hypolimnas missipus are nectar robbers. Fruits are woody capsules and remain attached on the plant even after flowering in the next season. The highest fruit yield (85%) was recorded in open pollinated conditions.