Swamp smartweed
Polygonum amphibium

Swamp smartweed reproduces using rhizomes (rootstocks) and seeds. Plants normally grow from 2' to 3' tall. The stems are usually unbranched and thicken to form nodes at the leaf joints. This trait is partially responsible for the common name of knotweed. Swamp smartweed may also exhibit a red-striped stem. The leaves of the plants are alternate, oblong, and tapering at both ends. They are usually pointed at the tip and exhibit smooth margins. The leaves of land plants grow up to 8" long, while those of aquatic plants are somewhat smaller (up to 6). The leaves of the land plants are generally more oval than those of aquatic plants, which exhibits floating, arrow-shaped leaves. The leaf stalks of both plant forms encircle the stem to form nodes. The plants display extensive root systems. They are known to grow roots at the nodes of the stem. Swamp smartweeds exhibit tall, slender, and erect flower clusters. The spike-like flower clusters grow from 1.5cm to 7cm tall normally much taller than 1. The flowers may be red, pink, or white (very rarely) in color. The species produces seed like fruit, which may be dark brown or black in color.