Many notorious alien invader are clonal plants,thus it is of great significance to understand the effect of clonal integra-tion on their potential invasiveness.This study investigated clonal integration (stolon connection) on the photosynthetic perform-ance,growth,competitive ability and biomass allocation of Alternanthera philoxeroides when it invaded the native Ludwigia pep-loides plant population,to explore the contribution of clonal integration on the invasion of this plant.We found that plant competi-tion significantly reduced the maximum quantum yield of photosystem Ⅱ,final biomass,ramet number and total stolon length of A.philoxeroides,whereas clonal integration greatly improved the photosynthetic performance,growth measures,significantly increased the competitive ability and root/shoot ratios of A.philoxeroides and facilitated its invasiveness.