 "R. undulatum") and "R. rhaponticum" were grown in Europe before the 18th century and used for medicinal purposes.By the early 18th century, these two species and a possible hybrid of unknown origin, "R." × "hybridum", were grown as vegetable crops in England and Scandinavia.They readily hybridize, and culinary rhubarb was developed by selecting open-pollinated seed, so that its precise origin is almost impossible to determine.