Although Eupatorium japonicum Thunb. is a threatened plant species in Japan, conservation ecological studies on it have not been enough for conservation practices. Conservation of threatened plant species requires information on seed germination and soil seed bank. In the present study, we conducted germination tests with gradual temperature method (GTM) considering the light conditions, aiming to evaluate the expression of physiological traits contributing to accumulate their seeds into soil seed banks. We also tried to germinate the seeds contained in the soil that was sampled within a habitat of this species in order to detect the soil seed bank. We found no germination traits contributing to accumulate their seeds into soil seed banks. We also could not detect their seeds in the soil within its habitat. We concluded that this plant does not have the mechanisms for soil seed bank formation. Therefore, if all of above-ground local populations will become extinct, it means extinction of this plants metapopulation. As we can not rely on soil seed banks for population restoration, our immediate task is to conserve the existing individuals and their habitats. When we should conduct the restoration of this plant, it is effective enough to disperse their cold-stratified seeds before the beginning of spring.
