This is a monster plant for the waterside, bearing enormous rounded leaves that look a little like rhubarb. Greenish flowers appear on naked stems in early spring. A bold, textural plant, it looks great beside a pond or stream. Place carefully: this is an aggressive spreader and difficult to eradicate once established. Spreading can be controlled by sinking a heavy plastic or metal tub into the ground and placing within. Plants will tolerate shallow standing water. Clumps may be divided in early spring. Young leaf stems are used as a vegetable in Japan.