Hawkmoth pollination of the African epiphytic orchid Mystacidium venosum, with special reference to flower and pollen longevity

The pollination biology of Mystacidium venosum Harv. ex Rolfe, an epiphytic orchid endemic to southern Africa, was investigated. The white flowers of this orchid have long spurs (c 4.5 cm) and contain dilute sucrose-dominated nectar which is secreted during the afternoon and early evening. Scent, dominated by Jasmine lactone and (E, E)-Farnesol, is emitted in the evening. A breeding system experiment established that self pollination results in inferior quality fruits. Field observations at three sites in Kwa-Zulu Natal, South Africa, in 1998 and 1999 showed that hawkmoths were frequent visitors to the orchid shortly after dusk, and carry pollinaria along the length of their tongues. No evidence for directional selection on spur length was found at any of the three sites. Results showed that flower longevity is strongly reduced by pollination, while pollinaria removal had only a small effect. Pollinia removed from flowers remained viable for up to 20 days under outdoor conditions.