Abstract:Aims Vallisneria species are very common and important in shallow lakes of the middle-lower reaches of the Yangtze River of China. Our objectives were to: 1) examine whether these co-existing Vallisneria species differ in sexual and clonal life- history traits, and 2) determine whether life-history traits explain the interspecific distribution pattern of these species. Methods Field investigations were carried out to determine the distribution and coexistence pattern of the three Vallisneria species (V. spinulosa, V. natans and V. denseserrulata) in lakes of the middle-lower reaches of the Yangtze River. Life-history traits of sexual reproduction and clonal propagation of V. spinulosa and V. natans were determined and compared under field condition and uniform glasshouse environment. Important findingsV. spinulosa was the dominant species in these lakes, V. natans was very common and V. denseserrulata was rare in this region. V. spinulosa and V. natans widely coexisted in these lakes; they frequently displayed a clear interspecific zonation pattern, or V. natans individuals scarcely occurred in V. spinulosa communities. Field investigations and glasshouse experiments suggested great differences of sexual and clonal life-history traits between V. spinulosa and V. natans. V. spinulosa is perennial, and capable of extensive clonal propagation, while V. natans is annual and reproduces mainly by sexual seedling as well as limited clonal growth. Differences of resource-acquisition and competitive abilities, caused by trade-offs of resource allocation between sexual reproduction and clonal propagation, might determine the pattern of competitive coexistence of V. spinulosa and V. natans.