Abstract: Reproductive allocation of biomass in Mikania micrantha H.B.K.populations from two different habitats,forest gap and open land,was studied at our field station in Dongguan City,China.From November to December 2004,samples were taken from blooming plants of M.micrantha at six different floral stages:bud emerging stage(Nov.1st),bud stage(Nov.12th),middle period of bud spreading(Nov.20th),blooming stage(Nov.29th),seed forming stage(Dec 9th),and seed maturation stage(Dec.24th).Reproductive allocation of biomass along with their relationship to the living environment from the two different habitats was examined at the modular and population levels.The results showed that during M.micrantha reproduction phases,both populations allocated predominant biomass to their vegetative growth,while the biomass allocated to reproductive growth displayed a relatively significant fluctuation.With ongoing reproductive phases,biomass allocated to inflorescence(RA)increased as a whole.During the six stages in our study,biomass allocated to vegetative shoots in the gap population was significantly less than that in the open land population,while the opposite occurred for reproductive shoots,except at the last two stages.Biomass allocated to inflorescence in the gap population was significantly greater than in the open land population through all the six stages.The results demonstrate that M.micrantha populations in gaps tend to use cloning as its reproduction strategy,while the population in open land uses sexual reproduction.