Butterfly pollination in Platycoryne (Orchidaceae): evidence for a key pollinator shift in the large Habenaria clade

Abstract

Shifts between pollinator functional groups can explain major changes in floral phenotype. I document a novel case of butterfly pollination in Platycoryne, an African genus that is phylogenetically embedded in the very large Habenaria clade in the Orchidaceae. Most Habenaria species have green or white flowers and many of these have been shown to be pollinated by moths, but my observations of the orange-flowered species Platycorynus mediocris in south-central Africa showed that it is pollinated diurnally by butterflies. The nectar-producing spurs of this species are c. 15 mm in length and closely match the tongue lengths of nymphalid and pierid butterflies that visit the flowers. The rostellum arms flank the spur entrance and place sickle-shaped pollinaria on the eyes or palps of the butterflies. In contrast to the highly scented flowers of moth-pollinated Habenaria species, the flowers of P. mediocris emit very little scent. Anecdotal observations indicate that several other Platycoryne species with orange flowers are also pollinated by butterflies. I conclude that the flower colouration (orange without UV reflectance) and low emission of scent in P. mediocris reflect an important historical shift to butterfly pollination in African members of the Habenaria clade.