Distribution of a naturalized weed, Barbarea vulgaris R. Br. in the Tohoku area of Japan.

Abstract

B. vulgaris is a naturalized weed that originated from Europe. Our questionnaire revealed that the species was found in all six prefectures of the Tohoku area in 1993 and 1996. From the distribution survey in 2001, we found that B. vulgaris had adapted to the area and had established itself as a weed throughout the Tohoku area. The weed abounded especially in the Aomori, Yokote, Kitakami, Sizukuishi, and Tohno regions. B. vulgaris has spread in the Yokote region during the past eight years. Most of the populations were found along the roadside and levees near irrigation canals for paddy fields. B. vulgaris also occurred on riverbanks and in levees where the bottom soil of irrigation canals had been deposited. Seeds submerged for 731 days still germinated, indicating that they could survive in water for two years. These results suggest that B. vulgaris is spread by the seed dispersed by water from irrigation canals and rivers