rhubarb plant MANSFELD:9537 Rheum is a genus of about 60 perennial plants in the family *Polygonaceae*. The genus includes the vegetable rhubarb (*Rheum rhabarbarum* or *Rheum x hybridum*). A number of varieties of rhubarb have been domesticated both as medicinal plants and for human consumption. While the leaves are toxic, the stalks are used in pies and other foods for their tart flavor. [https://en.wikipedia.org/wiki/Rheum_(plant)] rheum spp. knotweed family requires discussion