Reynoutria is a genus of flowering plants in the family Polygonaceae. It includes several species, commonly known as knotweeds, which are native to Asia and Europe. These plants are characterized by their hollow stems, large leaves, and clusters of small flowers. Some species, like Japanese knotweed (Reynoutria japonica), are known for their rapid growth and can become invasive in certain regions. The genus is often found in disturbed areas, such as riverbanks and roadsides, where they thrive in various soil types. Reynoutria species are used in traditional medicine and have applications in erosion control due to their extensive root systems. However, their invasive nature can lead to ecological challenges.