The Fireweed ludwigia (Ludwigia epilobioides) belongs to Onagraceae (the Evening primrose family). It is an annual herb that is distributed to various parts of Japan, as well as the Korean Peninsula, Southeast Asia, and India. It grows in paddy fields and wetlands and can reach 30-70 cm in height. The stems have ridges and are often reddish. The leaves are lanceolate and opposite, with prominent lateral veins. The leaves turn red in fall. From August to October, small yellow flowers come on the axils. Since the roots resemble "gobou" (burdock), it is also known as "ta-gobou" (paddy burdock) in Japan.