Abstract: Invasive plants often spread in their new range. Populations at the invasion front may evolve traits differing from those at the invasion center, such as small seed size, high germination rate, and fast germination speed. With 26 spreading Mikania micrantha  populations on Hainan Island, this study examined the evolution of seed size and germination traits. The results showed that germination rate of M. micrantha seeds was high (>70%). The cover and frequency of M. micrantha population and distance to invasion center were not significantly related to the mass of seeds collected both in the field and in the common garden experiment. Population cover was positively correlated with germination rate and germination index of seeds collected in the filed, but not with that of seeds collected in the common garden. Frequency and distance to invasion center were not significantly related to seed germination rate and germination index. Population cover, frequency and distance to invasion center were all not significantly related to seed germination speed. Overall, the evolutionary patterns of seed size and germination traits of M. micrantha populations during range expansion on Hainan Island were not obvious.

Key words: spread, density, germination, plant invasion, seed size