Alien Aquatic Plants Naturalized in Japan: History and Present Status

抄録

　Introduction of alien aquatic plants started in the Meiji Era (late 1800s) and some of them have been naturalized and caused serious weed problems in Japan. Eichhornia crassipes, Elodea nuttallii, Egeria densa and Pistia stratiotes have proven to be typical noxious aquatic weeds. The history of such in­vasive alien aquatic plants is briefly reviewed. Recently, more and more alien aquatic plants have been in­troduced due to a boom in aquarium and water gardening. Some of the newly introduced alien aquatic plants have begun to spread quickly. To date over 40 species have escaped and become naturalized in Japan. They threaten the biodiversity of native aquatic plants in various ways. The social backgrounds of the spread of alien aquatic plants are surveyed and the need for social education as well as legal regu­lation to discourage destructive activities are emphasized.