Reproductive biology of Epidendrum tridactylum (Orchidaceae: Epidendroideae): a reward-producing species and its deceptive flowers

Abstract

Epidendrum L. (Epidendroideae, Laeliinae) is one of the largest orchid genera distributed throughout tropical America. Based on data on reproductive phenology, floral morphology, labellar histochemistry, pollinators, pollination mechanisms and breeding system, this study explored the reproductive biology of Epidendrum tridactylum Lindl. growing in the state of Sao Paulo, southeastern Brazil. Epidendrum tridactylum produces an average of 87 rewardless flowers with a longitudinal protuberance on the median portion of its labellum, whose epidermal cells produce a pleasant citric fragrance. This fragrance attracts both male and female flies of families Calliphoridae, Sarcophagidae and Syrphidae that end up drinking the extrafloral nectar produced at the base of the bracts. Pollinaria are removed when the fly proboscis contacts the viscidium in search of nectar. After removing the pollinarium, the fly gets trapped in the flower, which frightens it, thus inhibiting any possible intent to immediately visit another flower and, at least presumably, reducing the possibility of geitonogamy. Since E. tridactylum is self-incompatible, the positive consequence of such behavior is a reduction of pollen loss. The fruits obtained through experimental cross-pollinations present highly variable percentages of potentially viable seeds. This is the first comprehensive study on the reproductive biology of a myophilous Epidendrum and a pioneer report of effective pollinators picking extrafloral nectar from Orchidaceae.