FLORAL BIOLOGY OF NEPENTHES-GRACILIS (NEPENTHACEAE) IN SUMATRA

Nepenthes gracilis, a dioecious carnivorous plant, has inconspicuous flowers lacking petals. Nectaries distributed on the upper surface of four sepals secrete dilute nectar (3%-12% sugar concentration) at night, but the nectar immediately disappears during the day by evaporation in the sunny environment of Sumatra. Male flowers have a higher nectar production rate but lower sugar concentration of nectar than female flowers. Flowers of both sexes were visited by pyralid moths at night and by calliphorid flies in the evening. Pollen was found attached on these insects visiting Nepenthes flowers. The pattern of nectar production of sepals is regarded as attracting nocturnal flying insects and avoiding ants, while the pitchers attract ants by nectar secreted on the pitcher rim.