Pollination biology of Aristolochia tagala, a rare species of medicinal importance

Abstract

Floral phenology, pollination biology and breeding system were studied in Aristolochia tagala Cham (Aristolochiaceae) grown under ex situ conditions. The flower exhibits structural features typical of fly-trap mechanism described for other Aristolochia species. Flowers show pronounced protogyny. Stigmas are receptive at anthesis and remain so for 24 h. Anthers dehisce 45– 48 h after anthesis by which time stigma receptivity is lost. Chironomid fly (Diptera) is the pollinator. Attracted by the odour and colour of the flower, the flies enter it and are detained in the chamber of the perianthtube (where the anthers and stigma are located) for nearly 50 h. Their escape is prevented by the presence of dense downward-pointing hairs in the perianth tube. The nectaries provide food to the insects. Following anther dehiscence, the thorax of the flies becomes loaded with sticky pollen grains. Hairs on the inner wall of the perianth tube wither and facilitate the exit of the flies. When a fly carrying the pollen load enters a fresh flower, it brings about pollination. Manual pollinations showed that the species permits geitonogamous pollination. The percentage of fruit set in manually pollinated flowers is higher than that resulting from open pollination, confirming that pollination is a limitation for fruit set in the ex situ-grown population. Nevertheless, fruit and seed set is sufficiently high for ex situ conservation purposes.