Ploidy level of the invasive weed Rubus alceifolius (Rosaceae) in its native range and in areas of introduction

 A change in ploidy level could increase invasiveness of introduced plants in insular plant communities. To examine this question for R. alceifolius, we compared its ploidy level in its Asian native range and in the Indian Ocean islands where it has been introduced. We first counted chromosomes on root tips from a Vietnamese individual, which proved to be tetraploid (2n=4x=28). The nuclear DNA content of other individuals from the native range and areas of introduction was estimated using the flow cytometry method. The Vietnamese individual on which chromosomes were counted was added to the sample, to enable deduction of the ploidy level of all individuals from their nuclear DNA content. All individuals were found to be tetraploid, except 10 individuals from a single clone collected in a Vietnamese population, estimated to be triploid, and morphologically different of other individuals of this study. We showed that while polyploidy of the source population may have predisposed this plant to become a successful invader, its introduction into Indian Ocean islands was not associated with any change in ploidy level. Received January 23, 2001 Accepted May 22, 2001