Reproduction determines the fitness and is a crucial component of life history. Asexual and sexual reproduction synergistically contribute to the fitness of clonal plants. Extreme warming leads to a periodical sharp rise in temperature and may affect the plant fitness. Few studies have concerned the impacts of extreme warming on the reproductive pattern of clonal aquatic plant and its evolutionary implication. In the present study, the cosmopolitan clonal submerged plant species, Potamogeton crispus L. from four different geographic sources, was subjected to simulated extreme warming. Both asexual and sexual reproductive performances including the recruitment of turions and fruits were evaluated. We found that both geographic source and warming significantly affected the reproductive performances. Although the response of turion number to warming was different for populations from different geographic sources, the turion mass did not decrease under warming. Moreover, warming induced a lower percentage of oligophyllous turions -- the turion with no more than four scale leaves each, and a higher percentage of pleiophyllous turions -- the turion with more than four scale leaves each. Additionally, warming caused a complete loss of sex for three populations. As the scale leaf functions as storage and photosynthetic organ and the scale leaf number is positively correlated with the axillary bud number, P. crispus may select to enhance the sprouting potential of turion to achieve the fitness optimization by enhancing the recruitment of scale leaves and thus larger turions under warming.