Rhubarb's story is one of the most unusual in this atlas: it is an ingredient that spent the great majority of its documented human history as medicine rather than food, whose journey from the imperial apothecaries of Tang Dynasty China to the kitchen gardens of Georgian England took more than two thousand years, and in which the transformation from root medicine to stalk pudding was driven not by any discovery about the plant's edibility but by the declining cost of sugar in 18th-century Britain. To understand rhubarb in the kitchen, one must first understand what it was before it entered the kitchen at all.

The genus Rheum (family Polygonaceae, the dock and knotweed family) encompasses roughly sixty species distributed across the highlands of Central Asia, the Himalayas, and the western Chinese mountain ranges. Three species are central to rhubarb's history. Rheum palmatum (Chinese rhubarb, 大黄 dà huáng, 'big yellow') and Rheum officinale (officinal rhubarb) are the two species native to the highlands of Sichuan, Qinghai, Gansu, and the eastern Tibetan plateau; their rhizomes (root-stocks) contain a complex mixture of anthraquinone glycosides that produce powerful cathartic and purgative effects. These are the species documented in the Shennong Bencao Jing (神農本草經, the Divine Farmer's Materia Medica, c. 200 BCE but recording knowledge attributed to the legendary emperor Shennong, c. 2700 BCE), the foundational text of Chinese herbal medicine, in which dà huáng is listed as one of the fifty fundamental medicinal herbs. Rheum rhaponticum (Pontic rhubarb) is the third species and occupies a different geography entirely: it is native to the Pontic steppes and the Caucasus highlands around the Black Sea, in the territory the ancient Greeks and Romans knew as Scythia, and it was this species that gave rhubarb its name. The river the Scythians and Greeks called 'Rha' (identified with the modern Volga or its tributaries, or sometimes with the Don or the river system of the Caucasus), along whose banks R. rhaponticum grew wild, lent the plant its classical name: rha pontikon (Pontic rhubarb) or rha barbarum (the rhubarb from the barbarian lands beyond the Pontus), which became the medieval Latin rhabarbarum and the English 'rhubarb'. Rheum rhaponticum is the second parent, alongside R. rhabarbarum, of the modern garden rhubarb hybrid (R. × hybridum) that is grown for its edible stalks today.

The edible stalks of garden rhubarb are not the stalks of any of these three ancestral species. The culinary rhubarb that fills pies, jams, crumbles, and compotes across the Northern Hemisphere is a hybrid, Rheum × hybridum, developed through centuries of horticultural selection from the crossing of R. rhaponticum (Pontic) and R. rhabarbarum (a broader cultivated group) in European botanical gardens. The stalks of the ancestral wild species are not particularly palatable in the way that the hybrid's stalks are; what changed was both the plant, through selection, and the context, through the availability of sugar. The critical enabling condition for rhubarb's transition from medicine to food was the fall in sugar prices in 18th-century Britain following colonial sugar production in the Caribbean: before sugar became affordable, the stalk's extreme tartness (driven by high malic and oxalic acid content) made it unpleasant to eat in any quantity; once sugar was cheap enough to sweeten a large pot of stewed rhubarb, the plant's distinctive sharp flavour became an asset rather than an obstacle.

A necessary note on the rhubarb leaf: it is toxic and must never be eaten. The leaf blade contains oxalic acid at concentrations many times higher than the stalk, enough to cause kidney damage and potentially death if consumed in quantity. The leaf base (where stalk meets leaf) is also best discarded. Only the stalk — the pink, red, or pale green fleshy stem — is eaten, and always cooked and sweetened for culinary purposes. This entry deals exclusively with the edible stalk and its culinary history; the medicinal uses of the root (which remain clinically relevant in Chinese and integrative medicine) are noted for historical context.

The global journey of rhubarb falls into two entirely distinct phases, separated by roughly two thousand years: the first a movement of the dried root as one of the most expensive medicinal substances in the known world; the second a movement of the living plant and its fresh stalks as a kitchen ingredient. The two phases barely overlap, and the ingredient that entered the British kitchen in the 1770s was related to the root that Venetian spice merchants sold by the scruple in the 1370s only in that both came from the same genus of plants.

The first phase — the medicinal trade — had its origin in the documented use of dà huáng root in Chinese medicine. Chinese physicians valued the dried, powdered rhizome as one of the most reliable and potent cathartics available; it appears in the Shennong Bencao Jing and in every subsequent major Chinese pharmacopoeia, classified by temperature, flavour, and organ affinity according to the system of traditional Chinese medicine. The root was a significant export item from China from at least the Han Dynasty period (206 BCE – 220 CE), moving westward along the Silk Road through Central Asia and Persia: the Persian word for it, rīvās (ریواس), entered the language early, and Persian physicians of the Sassanid period were acquainted with the plant's medicinal properties. A further complication is that in Persian and wider Middle Eastern usage, the word rīvās also refers to the stalks of the related native species Rheum ribes, which grows wild through Turkey, northern Iran, and the Caucasus and whose fresh stalks have been eaten raw with salt or cooked into meat stews (the khoresh-e rivas) for centuries: this is a genuinely different culinary tradition, predating European stalk-eating by many centuries, though it remained confined to the region and never became the global food that the British culinary tradition of the stalk would eventually produce.

From Persia the root trade passed to the Arab physicians of the Abbasid Caliphate, where Ibn Sina (Avicenna, 980–1037 CE) described it in the Canon of Medicine as rāwand, listing its purgative, anti-inflammatory, and liver-cleansing properties. From the Islamic world it entered Europe through the Venetian spice trade: the root arrived in Venice by the 13th and 14th centuries as one of the most expensive commodities in the spice market, priced higher than cinnamon and sometimes rivalling saffron in value by weight. Its expense derived partly from rarity (it grew only in remote Chinese highlands, far from any existing trade infrastructure) and partly from the secrecy that Chinese and Central Asian middlemen maintained around its source. Marco Polo, who travelled through Central Asia and China between 1271 and 1295, is among the first European writers to describe the plant growing in its native habitat and to report on its cultivation; his accounts contributed to European knowledge of the plant's Chinese origin, though the trade routes remained firmly in Chinese and Central Asian control for several more centuries.

The second great shift in the rhubarb trade came with the Russian Empire. From the late 17th century, the Russian state established a direct overland trade with China through the Siberian border post of Kyakhta, and the government quickly recognised that rhubarb root — for which there was insatiable European medical demand — was among the most valuable goods available in that exchange. The Russian Crown established the Rhubarb Office (Rabarber-kantselaryia) in 1731, making the import and sale of rhubarb root a state monopoly. Only root that passed quality inspection by government physicians was allowed to enter Western European markets under the Russian certification, and the monopoly price was set accordingly; inferior root was destroyed. The Russian rhubarb monopoly, which lasted until the 1780s when it was gradually relaxed, effectively made Russia the gatekeeper of the European medicinal supply for several generations, and the profits financed a not inconsiderable portion of the Russian state budget.

The transition to culinary use happened not in Russia or in the spice-trading cities of Europe but in Britain, and it happened when the cost of sugar fell far enough to make the tart stalk's sweetening affordable. The earliest English recipe using rhubarb stalks as a food rather than a medicine is generally placed in the 1740s; the botanist Richard Bradley had described the stalk's potential culinary use in the 1720s; and by the 1770s rhubarb was being grown in British kitchen gardens specifically for its stalks, with varieties selected for flavour and colour rather than medicinal root quality. The American colonies received the plant soon after: rhubarb is documented in American gardens from the 1770s onward, and 'pie plant' — the American vernacular name that reveals exactly what it was for — became established in New England and the Midwest through the early decades of the 19th century.

The final and most distinctive chapter of the British rhubarb story is forced rhubarb, developed in the area around Wakefield, Leeds, and Bradford in the West Riding of Yorkshire from the 1870s onward. Forcing had been practised on a small scale since at least the 1840s, but it was the combination of cheap coal for heating, the proximity of the textile mills that produced woollen waste as a ready fertiliser, and the discovery that complete darkness produced exceptionally tender and sweet stalks that turned the West Riding into what became known as the Rhubarb Triangle. In the peaked forcing sheds, rhubarb crowns were brought in from the cold after a period of frost (essential to break dormancy) and grown in total darkness heated by coal-fired boilers; the stalks, reaching for non-existent light, grew pale pink and bright crimson rather than their normal deep red, had a much more delicate flavour and texture than outdoor rhubarb, and could be harvested in the dead of winter when no other fresh fruit or vegetable was available. At the triangle's peak in the 1930s, it produced the majority of the world's supply of forced rhubarb, and the first tender stalks of the January harvest were still being transported to London markets by special night trains — 'the rhubarb express' — in the 1950s. Forced Yorkshire rhubarb now holds Protected Designation of Origin (PDO) status under UK law.

Rhubarb is grown commercially and in kitchen gardens across the temperate zones of the Northern and Southern Hemispheres, with Britain, the United States, Norway, Germany, and Canada among the largest producers of the culinary stalk. Yorkshire forced rhubarb remains a prized seasonal product, harvested between January and March and commanding a significant premium; outdoor rhubarb follows from April to July. The plant is a hardy, deep-rooted perennial that is easy to establish and difficult to kill, which accounts for its enduring presence in domestic kitchen gardens across the British Commonwealth and former settler-colonial territories; it is a common survivor in abandoned garden plots, its large, tropical-looking leaves marking old homesteads long after the houses have gone.

Culinary uses of the stalk divide broadly into four traditions. The British tradition — the oldest and still the most extensive — centres on stewed rhubarb as a filling or component for pies, crumbles, fools, trifles, and jams; the rhubarb crumble and the rhubarb fool are its most enduring expressions. The American tradition, built on the 'pie plant' inheritance, is dominated by rhubarb pie (often combined with strawberry, the two complementing each other in season) and, increasingly, by rhubarb in cakes, muffins, and quick breads. The Scandinavian tradition, particularly strong in Norway and Denmark, uses rhubarb in compotes, cordials, soups, and cold-weather preserves; the Norwegian rabarbragrot (rhubarb porridge/compote) and the Scandinavian rhubarb cordial are among the freshest, most elegant expressions of the plant's tart character. The German and Central European tradition, sustaining one of the largest rhubarb cultures in the world, turns the spring stalk above all into cake: the Rhabarberkuchen of every German household and Konditorei, in its streusel-topped and meringue-crowned forms, alongside the Rhabarberschorle cordial that is a favourite German summer refreshment.

Beyond the Western traditions, the Persian and Turkish culinary use of rhubarb stalks in savoury meat stews (khoresh-e rivas in Iran, rıbas stew in Turkey) represents the most ancient continuous culinary tradition of the stalk anywhere in the world — predating British pie-making by many centuries — though this tradition is based on the native Rheum ribes rather than the European garden hybrid. The stalks are used here entirely differently from the Western dessert tradition: uncooked, they may be dipped in salt and eaten raw as a snack or relish; cooked, they melt into the braising liquid of a lamb stew, providing the characteristic sweet-sour note that is the signature of the Persian khoresh genre.