Polygonum is a genus of about 220 species of flowering plant in the buckwheat and knotweed family Polygonaceae. 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 (Fagopyrum esculentum) has sometimes been included in the genus as Polygonum fagopyrum.