Rhizome dynamics in Calystegia japonica Choisy and Calystegia hederacea Wall. in relation to overwintering

Calystegia japonica Choisy and Calystegia hederacea Wall., common perennial weeds throughout cropped and uncropped land in Japan, are known to regenerate mostly by rhizomes. The rhizome dynamics of the two species were investigated, focusing on their overwintering characteristics. The dry weight of rhizomes continued to increase for 6–7 weeks after the decrease in weight of the aerial parts began, then it decreased in winter because of the partial death and consequent fragmentation of the rhizomes. Overwintering as naturally fragmented rhizomes is a unique characteristic of the two Calystegia spp. as it is not observed in other rhizomatous weeds that maintain systematic connections at least during the following regeneration in spring. In C. japonica , rhizome degradation was more pronounced and more systematic than in C. hederacea , where thicker fragments that included apices remained. Qualitative changes in C. japonica rhizomes, such as increases in dry matter accumulation and starch, and a temporary decrease in sprouting ability, seem to relate to this specialized survival mechanism. Calystegia hederacea did not show either specialization or preparation for overwintering in its rhizome. The adaptability of Calystegia weeds to annual crop fields can be attributed to their capacity to regenerate from naturally fragmented rhizomes.