Persicaria japonica is
a perennial occurring in wetlands, the stems erecting 0.5-1m in
height, having underground stems also, which put forth new growths.
Leaves, with short petioles, are lanceolate, acuminate, 7-16cm in
length, and the basal parts wedge-shaped. Inflorescences are spike-like,
l5-10cm in length, and drooping the ends. Flowers are white and
small, 3-4mm in diameter. Bloom time: August-October.