Flowering patterns and pollination syndromes were compared among four sympatric Impatiens species (Balsaminaceae) in tropical montane rain forests in Sumatra, Indonesia. Pink flowers with long filiform spurs of I. platypetala produced nectar of 26 % sugar both in the daytime and at night and were po11inated by crepuscular hawkmoths, Macroglossum corythus. Yellow flowers with gradually tapering spurs of I. korthalsii, I. talangensis and I. eubotrya produced nectar of 34-39 % sugar, mainly in the daytime, and were po11inated by two specialized long-tongued anthophorid bees and an unusually long-tongued halictid bee. Spur morphology essentially determined nectar accessibility. Although the three Impatiens species partially shared the three bee species, they partitioned their po11inators by differing in sites of pollen deposition on the bee's bodies. The low po11inator visitation rates per day were compensated by the extended flowering period of the four species. Nectar robbing by two anthophorid bee species was observed, for the first time in Southeast Asia.