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

Floral phenology, pollination biology and breeding sys tem were studied in Aristolochia tagala Cham. (Aristo lochiaceae) grown under ex situ conditions. The flower exhibits structural features typical of fly-trap mecha nism 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. At tracted by the odour and cobur of the flower, the flies enter it and are detained in the chamber of the perianth tube (where the anthers and stigma are located) for nearly 50 h. Their escape is prevented by the pres ence of dense downward-pointing hairs in the peri anth 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 re sulting from open pollination, confirming that pollina tion is a limitation for fruit set in the ex situ-grown population. Nevertheless, fruit and seed set t is suffici ently high for ex situ conservation purposes.