Mirror-image flowers without buzz pollination in the Asian endemic Hiptage benghalensis (Malpighiaceae)

Abstract

Mirror-image flowers represent a highly specialized pollination system that is normally associated with poricidal anthers and buzz pollination (pollen can be only released from anthers via pollinator vibration). In the Asian endemic Hiptage benghalensis (Malpighiaceae), mirror-image flowers were found with longitudinally dehiscing anthers and such floral syndromes are firstly reported in the family. We investigated the floral biology and frequencies of left- and right-styled flowers of H.benghalensis in Hainan Island, southern China. We conducted pollination manipulations to determine breeding systems and studied the pollination mechanism. We also examined the compositions of the secretions of the calyx gland. Controlled pollinations revealed that H.benghalensis is self-compatible. Left- and right-styled flowers are produced in the same inflorescence and a 1:1 ratio is found at both plant and population levels. Flowers have extremely reflexed petals, zygomorphic corollas and a single but oversized calyx gland. This gland secretes sugars and mainly attracts ants and wasps in both blooming and fruiting periods. Heteranthery is obvious with one large stamen producing more viable pollen than the nine small stamens. All anthers dehisce longitudinally and pollen grains readily adhere to floral visitors without the need of buzz pollination. The unusual association of mirror-image flowers with longitudinal anthers probably reflects an adaptation to local pollen-collecting (but non-buzzing) honeybees such as Apis dorsata. These results indicate that floral syndromes and pollination adaptation in H.benghalensis differ completely from the New World Malpighiaceae and may help to explain evolutionary adaptations of the family during its long-distance dispersals from the New World to Asia. © 2013 The Linnean Society of London.