Calamus javensis is a widespread understorey rattan in Southeast Asia and is one of the dominant rattan species in Mt. Halimun National Park West Java. This species can establish clumps either sexually with seeds or clonality with stolons. To analyze the role of sexual reproduction and clonality for clump establishment in C. javensis we studied the vegetative and genetic structures of the population. Totals of 2777 ramets comprising 1321 clumps were found in three 0.16 ha plots. The number of ramets per clump showed reverse J-shaped distribution with a maximum of 15. Clustering and stoloniferous ramets accounted for 62 and 20% of all ramets respectively. This indicates that C. javensis is actively engaged in clustering clonal growth. The longest stem was 14 m although 75% of all stems were shorter than 1 m long. The stolon ranged from 6 to 538 cm in length which decreased the local density of ramets. Using randomly amplified polymorphic DNA (RAPD) analysis we obtained 56 polymorphic bands for 118 clumps sampled from one of the plots. All samples showed different RAPD banding patterns except one pair at a distance of 225 cm from each other. The genetic similarity among samples closer than 10 m was significantly higher than the expected value from a purely random distribution. These results suggest that most separate clumps are established by recruitment from seeds and most seeds dispersed near mother plants. Hence in C. javensis clonality is more a growth strategy to increase the size of the genet than a dispersion-propagation strategy to expand the habitat. [ABSTRACT FROM AUTHOR]