Clonal integration facilitates the expansion of Hydrocotyle vulgaris from a limited space to a larger area

Clonal integration is an important ecological advantage of clonal plants. To ask whether clonal integration can help invasive plants escape space limitations, we tested the hypothesis that it can promote the growth of apical ramets when their connected basal ramets grow in limited space. We conducted a greenhouse experiment on the common perennial herb Hydrocotyle vulgaris. Clonal fragments consisting of pairs of connected ramets grew with basal ramets in three different sizes of pots (small, medium, and large) and apical ramets in large pots, and the connection between ramets was either severed or left intact. Pot size significantly affected the growth of basal ramets such that the biomass, number of leaves and flowers, and stolon length were in general greater in medium pots than in large and small pots when stolons were intact and were greater in medium and large pots than in small pots when stolons were severed. Furthermore, pot size interacted with severance to affect the performance of H. vulgaris. When the basal ramets grew in small pots, the intact stolon resulted in a significant promotion of apical ramet growth, but such positive effect was not found when the basal ramets grew in medium and large pots. Our results suggest that H. vulgaris is able to promote the growth of apical ramets to occupy the surrounding areas through clonal integration when the space where basal ramets grow is limited.