Rhubarb is an odd food plant: we only eat the leaf stems.
I guess the same is true for celery, but celery leaves and roots are edible. Rhubarb leaves could kill you. Rhubarb roots were a significant traditional herbal medicine all across Eurasia, often as a purgative. So this food plant is raised only for its leaf stems (technically, petioles).
How Rhubarb Was Named
Rhubarb is Rheum in the buckwheat family, Polygonaceae. The Plant List recognizes 43 valid species, and while clearly some are obscure wild plants, many are in cultivation. Various species have been used as medicines. The garden rhubarb we eat is a hybrid of murky origin. Other species are grown as attractive perennials.
The genus name, Rheum, comes from the Greek, but whether it is from Rha, an old name for the Volga River which was probably the source of the rhubarb sold in ancient Greece or from the Greek rheo, to flow, referring to its purgative qualities, is unclear. Dioscorides, 64 CE, a Greek physician working in the Roman armies, in a very influential herbal gave both the names reon and rha for rhubarb, and likely Linnaeus referred to Dioscorides when choosing its scientific name. Rheum rhaponticum, sometimes called rhaponticum rhubarb, is native to Asia Minor with one known population in Europe, and was almost certainly the rhubarb of Greek and Roman writers. Dioscorides described using the root and its powder for a variety of ailments, especially as a tonic for the stomach. It was imported to Europe from the Middle East and likely from central Asia as well.
The English word rhubarb is apparently an English version of its French name, reubarb. The name appeared as early as 1300 CE, so the plant has been known in England at least that long. In English works from around 1600, for example Gerard’s Herball and Hill’s garden book, A Gardener’s Labyrith, it was spelled rubarb and ruberb more than rhubarb. I wonder what helpful dictionary writer stuck us with the h.
Rhubarb in bloom
Uses Through The Ages
By the European Middle Ages, rhubarb was a well-known medicine, used for the gentle laxative from its root. Small doses of rhubarb root powder halt diarrhea while large doses will purge the intestines.
As a root or dry powder rhubarb traveled easily all across Eurasia. The various species differed in their potency, so by late medieval times, writers of herbals discussed the efficacy of the different types, usually in terms of their place of origin.
Planted together, whether in Asia or Europe, the rhubarbs, Rheum palmatum and R. officinale of China, R. rhaponticum of Asia Minor, R. rhabarbum of Mongolia and others, hybridized and sometimes doubled their chromosomes. The hybrids often had poor seed production or the seedlings would lack the desirable characteristics of their parents. This led to people propagating rhubarb via pieces of root. My sources today call garden rhubarb Rheum x hybridum, R. rhabarbum, and R. rhaponicum, reflecting the confusion of a collection of hybrids and clones.
Learn more about rhubarb in part 2!
Gerard, J. 1636. The Herball or General Historie of Plantes. London. Adam Norton and John Whitaker. Lib. 2, Chap. 83 Of Rubarb online
Gunther, R. T. editor. 1934. The Greek Herbal of Dioscorides, originally 64 CE. The University Press. Oxford.
Hill, T. 1987. The Gardener’s Labyrinth, originally 1577. edited by R. Mabey. Oxford University Press, Oxford.
Libert, B. and R. Englund. 1989. Present distribution and ecology of Rheum rhaponticum (Polygonaceae). Willdenowia 19: 91-98.
The Plant List (2013). Version 1.1. http://www.theplantlist.org/ (accessed 10/3/17).
Rhubarb. Oxford English Dictionary online. September 30, 2017
van Wyk, B-E. 2005. Food Plants of the World. Timber Press, Portland, OR.