water smartweed (Plants of Saxony)

water smartweed

Persicaria amphibia

Summary ⁷

Persicaria amphibia (syn. Polygonum amphibium) is a species of flowering plant in the knotweed family known by several common names, including longroot smartweed, water knotweed, water smartweed, and amphibious bistort. It is native to much of North America, Asia, Europe, and parts of Africa, and it is known elsewhere as an introduced species and sometimes a noxious weed.

Description ⁸

This perennial plant is about 2–3½' tall and either unbranched or sparingly branched. The central stem is more or less erect (for terrestrial plants), swelling somewhat at the nodes where the leaf-sheaths wrap around the stem. These nodes can be brownish and short-hairy, but they lack bristles at the edges. Otherwise, the central stem is light green, terete, and glabrous to silky-hairy. The alternate leaves are up to 8" long and 3" across; they have short petioles. The leaves are usually lanceolate or ovate in shape, while their margins are smooth. Sometimes the margins are undulate (up-and-down) or slightly curled. Both the upper and lower leaf surfaces are medium green. The leaf surfaces are either hairless, or they have appressed silvery hairs, depending on the local ecotype. The midveins on leaf undersides are quite prominent. Their are 1 or 2 terminal racemes of flowers at the apex of the central stem. The flowering stalks are quite hairy and often brownish in appearance. The cylindrical racemes are about 2-3" long and densely crowded with flowers. Each flower is about 1/6" (4-5 mm.) across, consisting of 5 petaloid sepals, 5 exerted stamens, and an ovary with a divided white style. The showy sepals of these flowers are rosy pink or scarlet (usually the former). The blooming period can occur from mid-summer to early fall, lasting about 1-2 months for a colony of plants. There is no noticeable floral scent. Usually, only a minority of plants in a colony will bloom during a given year. The flowers are replaced by black seeds that are ovoid to globoid in shape and somewhat flattened; the seed surface is shiny and minutely granular. The root system produces long rhizomes, from which colonies of plants are formed. Cultivation

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