Rheum L.
Rheum is a genus of ca. 30-60 species, chiefly distributed in temperate Asia. Some species are cultivated for ornamental or medicinal purposes or as vegetables. As a result of selection and hybridisation specific boundaries between certain species have become obscure and the exact identity of the species currently cultivated in W-Europe is somewhat uncertain. They are usually referred to as Rheum x rhabarbarum, a putative hybrid involving R. palmatum L. and R. rhaponticum L. However, Clement & Foster (1994) cite, in addition to this hybrid, also Rheum officinale Baillon and R. palmatum as occasional escapes from cultivation.
Literature:
Akeroyd J.R. (1989) Rheum. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 3. Cambridge University Press, Cambridge: 124.
Clement E.J. & Foster M.C. (1994) Alien plants of the British Isles. BSBI, London: XVIII + 590 p.