Floral ecology and pollination in Eriolaena lushingtonii (Sterculiaceae), an endemic and threatened deciduous tree species of southern peninsular India

Abstract

Eriolaena lushingtonii is an endemic and threatened medium-sized deciduous tree species. The flowering is very brief and occurs during the early wet season. The flowers are solitary, remain within the foliage and attract a few bee foragers only in the presence of nectariferous and polleniferous plants such as Holarrhena pubescens, Grewia tiliaefolia and Orthosiphon rubicundus which are common, exhibit gregarious flowering and attract a wide array of insects. In E. lushingtonii, the floral characteristics suggest entomophily but it is exclusively melittophilous involving Apis, Trigona and Xylocopa bees in the study area. The hermaphroditic flowers with the stigmatose style beyond the height of stamens and the sticky pollen grains do not facilitate autogamy but promote out-crossing. The study showed that pollinator limitation is responsible for the low fruit set but it is, however, compensated by multi-seeded fruits. Anther predation by a beetle also affects the reproductive success. Explosive fruit dehiscence and anemochory are special characteristics but these events are not effective during the wet season. The locals exploit the plant for treating snake bites, scorpion sting, making ropes and fuel wood. Therefore, the pollinator limitation, ineffective anemochory, seedling establishment problems and local uses largely contribute to the endemic and endangered status of E. lushingtonii.