Sunday, October 15, 2017

Plant Story--Rhubarb, A Curious Food

Rhubarb is an odd food plant: we only eat the leaf stems.

rhubarb
Rhubarb. Only the leaf stems are harvested and eaten!
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).



rhubarb stems
The part of rhubarb we eat.
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.

rhubarb

In China, the first written record of rhubarb, used as a medicine, was at least 5000 years ago. They used rhubarb medicinally under the name dà huáng, literally big yellow, referring to the root's size and the fact that the powder of the yellowish-red dried root stained the mouth yellow. Primarily it was used as a tonic for the blood, the digestive tract and for imbalances specific to women.

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 atleast 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

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.

Rhubarb leaves are quite poisonous. They contain dangerous concentrations of oxalic acid compounds. In low concentrations, oxalic acid tastes good to people, but the concentration of oxalic acid compounds in rhubarb leaf blades is much higher than that. People have died after eating cooked rhubarb leaves (About poisoning: NewYorkTimes , RhubarbInfo.comthePoisonGarden)

Using rhubarb for anything other than a medicine is quite recent. The earliest report I found was from the Bynums (reference below), who wrote that rhubarb leaf stems were sold as a novelty food at Covent Garden (link) in London in the early 19th century, but that it took the arrival of cheap sugar from the Indies to make rhubarb popular, since they are very tart. Grieve in her herbal reported people eating rhubarb leaf stems in England the 1830s and 40s. The food caught on and today, for many people "pie plant" is the usual name of rhubarb, in recognition of its main use.

rhubarb leaves and stem

Whether you want to call rhubarb a vegetable or a fruit depends on your use of the two words. In common language, vegetables are not sweet and are eaten in salads, soups, stews etc., while fruits are sweet and are eaten as dessert or as a sweet treat. Botanically, however, the fruit is the part of a plant that contains the seeds. Botanists apply the word vegetable to plant material generally, as in vegetable kingdom, so fruits are a particular vegetable structure. As you see: rhubarb comes out a fruit in common usage and a vegetable in botanical terminology. You have to like that whether you say fruit or vegetable, you will be both right and wrong at once.

Finally, consider this English riddle:

What is long and thin and covered in skin
Red in parts, stuck in tarts?

rhubarb

Rhubarb, of course.


Comments and corrections welcome.

References
Bynum, H. and W. Bynum. 2014. Remarkable Plants that Shape Our World. The University of Chicago Press, Chicago IL. 
Gerard, J. 1636. The Herball or General Historie of Plantes. London. Adam Norton and John Whitaker. Lib. 2, Chap. 83 Of Rubarb online
Grieve, M. 1971. A Modern Herbal. Originally 1932. Dover Publications, New York. online rhubarb
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.
Li, S-C. 1973. Chinese Medicinal Herbs. translated by F. P. Smith and G.A. Stuart. Dover Publications, New York.
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 Dicionary online. September 30, 2017
van Wyk, B-E. 2005. Food Plants of the World. Timber Press, Portland, OR.
Vickery, R. 1995. Oxford Dictionary of Plant-Lore. Oxford. Source of the rhubarb riddle.

Kathy Keeler, A Wandering Botanist
Join me on Facebook: https://www.facebook.com/AWanderingBotanist

Other vegetable and fruit stories in
Curious Stories of Familiar Plants from Around the World available from Amazon.com link



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