A dry extract from the roots of rhapontic rhubarb (extract Rheum rhaponticum (L.); ERr) has been commercially available in Germany for over two decades to treat menopausal symptoms. However, the molecular basis of its clinical effectiveness remains obscure. This article reviews the in vitro and in vivo data of its estrogenic actions, particularly those mediated by estrogen receptor-beta (ERbeta).

Oxalic acid is widely distributed in plants. Although its concentration is not normally high, certain plants such as Oxalis sp., Begonia sp., rhubarb, and spinach contain large amounts of the acid. Cotyledons of spinach, for example, have been reported to contain up to 26% dry weight of oxalic acid (4). The only enzyme system previously reported to metabolize oxalate in plants is oxalate oxidas...