Polygonum species are occasionally eaten by humans, and are used as food plants by the larvae of some Lepidoptera species - see list. Most species are considered weedy, especially in moist soils in the USA.The genus name is from the Greek poly = "many" and gonu = "knee" or "joint", in reference to the swollen jointed stem.The genus primarily grows in northern temperate regions. They vary widely from prostrate herbaceous annual plants under 5 cm (2 in) high to erect herbaceous perennial plants growing up to 3-4 m (10-13 ft) tall to perennial woody vines growing up to 20-30 m (66-98 ft) high in trees. Several are aquatic, growing as floating plants in ponds. The smooth-edged leaves range from 1-30 cm (0.39-11.81 in) long, and vary in shape between species from narrow lanceolate to oval, broad triangular, heart-shaped, or arrowhead forms. The stems are often reddish or red-speckled. The small flowers are, pink, white, or greenish, forming in summer in dense clusters from the leaf joints or stem apices.Polygonum is a genus in the Polygonaceae family. Common names include knotweed, knotgrass, bistort, tearthumb, mile-a-minute, smartweed and several others. In the Middle English glossary of herbs Alphita (c. 1400-1425), it was known as ars-smerte. There have been various opinions about how broadly the genus should be defined. For example, Buckwheat has sometimes been included in the genus.
Several species can be eaten cooked, for example during famines. The species Polygonum cognatum, known locally as "madimak", is regularly consumed in central parts of Turkey.
In Chinese medicine, a Polygonum extract called Rèlínqīng Klì (-) is used to treat urinary tract infections. Chinese medicine also uses a Polygonum multiflorum extract called Fo-Ti.
Care should be taken not to confuse Polygonum with Polygonatum - an entirely different genus of plants.
In The Man Who Laughs Victor Hugo wrote of the Comprachicos (child-buyers) who created artificial dwarfs, formed "by anointing babies' spines with the grease of bats, moles and dormice" and using drugs such as "dwarf elder, knotgrass, and daisy juice". The idea of such use was also known to Shakespeare, as Beatrice K. Otto pointed out, quoting A Midsummer's Night Dream:
Between 65 and 300 species are recognised, depending on the circumscription of the genus; some botanists divide the genus into several smaller genera, including Fagopyrum, Fallopia and Persicaria.
The genus Polygonella has a number of morphological similarities with Polygonum, and some authors have included Polygonella in Polygonum.
Selected species include: