The dioecious, sphingophilous species Citharexylum myrianthum (Verbenaceae): Pollination and visitor diversity

Abstract

Citharexylum myrianthum is an example of cryptic dioecy in morphologically perfect flowers. Flowers are small, tubular, white-colored, and crepuscular, with a sweet, pleasant scent and occur in raceme-like inflorescences. Functionally, male flowers have a less developed ovary and females have anthers lacking pollen. They are pollinated by five species of Sphingidae. The low fruit set under natural conditions, compared with the very high fruit set after hand-pollination, apart from other possible factors, suggests that pollen flow is limited mainly by pollinators. The overabundance of nectar provided by C. myrianthum flowers attracts a large number of opportunistic nectar foragers in the morning. Hummingbirds, the most frequent visitors, are nectar thieves and display territorialism, being aggressive even to Passeriformes. Despite its visitor diversity C. myrianthum is pollinated by sphingids, and in this sense this species is a specialist rather than a generalist.