Ricinus

• 1. Introduction

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  Ricinus communis, the castor oil plant, bears seeds of which only four to eight are considered a lethal dose for an adult. Guinness World Records calls it the world's most poisonous common plant. Even so, reports of actual poisoning are relatively rare, and people have grown it, pressed it and rubbed its oil on their skin for thousands of years. It is the only species in its genus, Ricinus, and it belongs to the spurge family, Euphorbiaceae. Its seed is known as the castor bean. How can something this dangerous be so thoroughly woven into daily life? What separates the useful oil from the deadly seed? And who has put both to work, for good and for ill?

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• 2. A Shapeshifting Plant

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  Ricinus communis can reach about 12 metres, the height of a small tree, yet it is a fast-growing, suckering shrub that cannot tolerate cold. Its habit and appearance vary greatly, partly because breeders have selected cultivars for leaf colour, flower colour and oil production. The glossy leaves are 15-45 centimetres long, alternate and palmate, with five to twelve deep lobes. Each lobe has coarsely toothed edges.

  Some varieties begin with dark reddish purple or bronze young leaves that slowly turn dark green, sometimes with a reddish tinge. Others are green almost from the start. In a third group, a pigment masks the green of every chlorophyll-bearing part, so leaves, stems and young fruit stay purple to reddish brown for life. Dark and green plants can be found growing side by side, which suggests that a single gene controls the pigment in some varieties.

  The castor flower has no petals at all. Male and female flowers grow on the same plant, a habit botanists call monoecious, in terminal clusters that are green or, in some varieties, shades of red. The male flowers are numerous and yellowish-green, with prominent creamy stamens. The few female flowers sit at the tips of the spikes, inside immature spiny capsules, and show prominent red stigmas.

  The fruit is a spiny capsule, greenish or reddish purple, holding large, oval, shiny seeds with variable brownish mottling. In some varieties the capsules are more showy than the flowers.

  The cultivar Carmencita has won the Royal Horticultural Society's Award of Garden Merit. Its Bright Red form has red stems, dark purplish leaves and red seed pods, while Carmencita Pink has green leaves and pink pods. Gibsonii has red-tinged leaves with reddish veins and bright scarlet pods. New Zealand Purple has plum-coloured leaves tinged with red, and plum pods that turn red as they ripen. All of these grow to around 1.5 metres as annuals. Impala is compact at only 1.2 metres, and Zanzibarensis is tall, with mid-green leaves 50 centimetres long and white midribs.

  Sown early under glass and kept at around 20 degrees Celsius until planted out, a castor plant can reach 2-3 metres in a single year. Parks and other public areas use it extensively, particularly as a dot plant in traditional bedding schemes. Where frost is common it stays shorter and is grown as an annual. In southern England it can thrive outdoors, and in sheltered spots the leaves seem unharmed by frost and the plant stays evergreen. Toronto, Canada, used it in its parks in Edwardian times.

  The native range of castor covers the southeastern Mediterranean Basin, Eastern Africa and India, but today it is widespread across the tropics. Where the climate suits it, the plant establishes itself easily, can become invasive and often turns up on wasteland. In the United States it is not cultivated, yet it grows wild, notably in Griffith Park in Los Angeles.

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• 3. Ants, Spiders and Moths

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  A yellow nodule at one end of each castor seed is packed with fats that young ants find nutritious. This warty appendage is called the caruncle, a type of elaiosome. Ants haul the seeds into their nests, pull off the fatty part and dump the rest on a trash pile. There the future plant begins to grow. Botanists call this dispersal by ants myrmecochory.

  The jumping spider Evarcha culicivora has an association with castor. It drinks the plant's nectar for food and prefers castor plants as a place for courtship.

  Three species use Ricinus communis as a host plant: the common castor butterfly, Ariadne merione, the eri silkmoth, Samia cynthia ricini, and the castor semi-looper moth, Achaea janata. The larvae of other Lepidoptera also feed on it, including Hypercompe hambletoni and a moth called the nutmeg, Discestra trifolii.

  Selfing by geitonogamy is favoured in castor's mixed pollination system, meaning pollen tends to pass between flowers on the same plant. The plant can still outcross, though, through wind pollination or through visiting insects.

  People have recruited the castor leaf for caterpillars of their own. The Bodo tribe of Bodoland in Assam, India, feeds the leaves to the larvae of muga and endi silkworms.

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• 4. Ticks, Beavers and Christ

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  Carl Linnaeus chose the name Ricinus because it is the Latin word for a tick. The seed earned the comparison through the bump at its tip and the markings on its surface, which resemble certain ticks.

  The same genus name is also used in zoology, where it designates insects, not ticks, that live as parasites on birds. That overlap is possible because plants and animals are governed by different nomenclature codes.

  The seed is called a bean, but it is not one, since it does not come from a member of the family Fabaceae. A plant sold as the false castor oil plant, Fatsia japonica, is not closely related either. Researchers are currently studying the evolution of castor and its relatives with modern genetic tools.

  The common name probably comes from castoreum, a perfume base made from the dried perineal glands of the beaver, whose Latin name is castor. Castor oil seems to have served as a replacement for it. Another name, palm of Christ, or Palma Christi, refers to the oil's reputed ability to heal wounds and cure ailments. That reputation is far older than Linnaeus.

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• 5. Lamps and Laxatives

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  Egyptian tombs dating back to 4000 BC contain castor seeds. The slow-burning oil was mostly used to fuel lamps. Herodotus and other Greek travellers noted that it also served for lighting, body ointments and improving the growth and texture of hair. Cleopatra is reputed to have used it to brighten the whites of her eyes.

  The Ebers Papyrus, an Egyptian medical treatise believed to date from 1552 BC, describes castor oil as a laxative. It was translated in 1872.

  In India, castor oil is called eranda, and its use in lamps and local medicine has been documented since 2000 BC. Unani, Ayurvedic, siddha and other ethnomedical systems used it as a laxative, purgative and cathartic. Traditional Ayurvedic and siddha medicine considers it the king of medicinals for curing arthritic diseases. It is regularly given to children to treat infections with parasitic worms.

  The Roman naturalist Pliny the Elder cited the poisonous qualities of the seeds. He still described uses for them, noting that they could form wicks for oil lamps, possibly when crushed together. He also named the oil as a laxative and as lamp oil. For the leaves he gave a longer list. Applied with vinegar they treated erysipelas, and a decoction in wine with polenta and saffron was good for inflammations. He wrote that, boiled by themselves and applied to the face for three successive days, "they improve the complexion."

  In Haiti the plant is called maskreti and is turned into a red oil. It is given to newborns as a purgative to cleanse the insides of their first stools. In China, castor seed and oil have been prescribed for centuries, mainly in local medicine, either for internal use or in dressings. The laxative effect so prized in all these traditions would later be turned into a weapon.

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• 6. An Instrument of Coercion

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  The paramilitary Blackshirts under the Italian dictator Benito Mussolini used castor oil as an instrument of coercion. The Spanish Civil Guard did the same in Francoist Spain. Dissidents and regime opponents were forced to swallow the oil in large amounts.

  The result was severe diarrhea and dehydration, which could ultimately cause death. The punishment was originally thought up by Gabriele D'Annunzio, the Italian poet and Fascist supporter, during the First World War.

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• 7. Poison and Pollen

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  Ricin, a highly potent water-soluble toxin, is the reason raw castor beans are dangerous, and it is present in lower concentrations throughout the rest of the plant. After ingestion, symptoms commonly begin within two to four hours, though they may be delayed by up to 36 hours. They start with a burning sensation in the mouth and throat, abdominal pain, purging and bloody diarrhea. Within several days come severe dehydration, a drop in blood pressure and a decrease in urine. Unless treated, death can be expected within 3-5 days, but in most cases a full recovery is made.

  Intact seeds may pass through the digestive tract without releasing any toxin. Poisoning happens when animals, including humans, swallow broken seeds or break them by chewing. That is why castor beans can be strung into cheap, non-durable necklaces and bracelets, but only if no holes are drilled. The outer shell protects the wearer, and any chip in it can cause poisoning. Wearing the beans has been known to cause rashes, and pets that chew the jewellery can become ill.

  The toxin also gives the plant some natural protection from insect pests such as aphids, and ricin has been investigated for use as an insecticide. An extract of the plant showed acaricidal and insecticidal activity against adults of Haemaphysalis bispinosa, a tick, and Hippobosca maculata, a blood-feeding fly. Cold-pressed castor oil sold commercially is not toxic to humans in normal doses, whether taken internally or used on the skin.

  On the OPALS allergy scale, Ricinus rates 10 out of 10. It is also a very strong trigger for asthma, and allergies to it are commonplace and severe. The plant produces abundant, very light pollen that easily becomes airborne and can be inhaled into the lungs. Its sap causes skin rashes, and people allergic to the plant can develop rashes from touching its leaves, flowers or seeds. They can also react to the latex sap of the related Hevea brasiliensis.

  Laboratory work has found three terpenoids and a tocopherol-related compound in the aerial parts of Ricinus. In root extracts, two triterpenes were enriched: lupeol and urs-6-ene-3,16-dione, also called erandone. At doses of 100 mg/kg, the crude methanol extract, the enriched n-hexane fraction and the isolates showed significant anti-inflammatory activity in a carrageenan-induced hind paw oedema model.

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• 8. Fields and Factories

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  India produced 1,196,680 tonnes of castor seed in 2019, out of a world total of 1,407,588 tonnes in the same table. Mozambique came next with 85,089 tonnes, followed by China with 36,000. Other estimates put yearly global production around two million tons, with India supplying over three-quarters. Castor is also widely grown as a crop in Ethiopia, and several breeding programmes are active.

  The seeds hold 40-60 percent oil, rich in triglycerides, mainly ricinolein. Breeders have tuned cultivars for that oil. 'Hale' was launched in the 1970s for Texas. It is short, up to 1.2 metres, with several racemes. 'Brigham', also adapted for Texas, grows up to 1.8 metres and carries only 10 percent of the ricin of 'Hale'.

  Brazil's Embrapa developed 'BRS Nordestina' in 1990 for hand harvest in semi-arid environments, and 'BRS Energia' in 2004 for mechanised or hand harvest. In India, Sardarkrushinagar Dantiwada University released 'GCH5' in 1995, resistant to fusarium wilt. Its 2004 successor 'GCH6' resists root rot and tolerates fusarium wilt. In Ethiopia, research centres produced 'Abaro' and 'Hiruy' for hand harvest, with 'Hiruy' following during 2010/2011.

  Castor oil is an effective motor lubricant. It served in the internal combustion engines of World War I airplanes, some racing cars and some model airplanes. It was historically popular in two-stroke engines because it resists heat better than petroleum-based oils. It mixes poorly with petroleum products, especially in the cold, but blends better with the methanol-based fuels of glow model engines. It leaves carbon deposits and varnish in total-loss applications, and synthetic oils that are more stable and less toxic have largely replaced it.

  In chocolate factories, polyglycerol polyricinoleate, made mainly from castor oil, improves the flow of cocoa butter in bars and reduces costs. Castor derivatives also appear in cosmetics and in ointments, because the ricinoleic acid they contain inhibits many viruses, bacteria and fungi. Other products serve as non-freezing, pressure-resistant lubricants, chemical feedstocks and raw material for some biodiesel. Gardeners use castor as a repellent for moles and voles in lawns.

  In Asia, castor leaves are used in botanical printing, also called ecoprinting. Bundled with cotton or silk and steamed, they leave a green imprint.

  In traditional Nigerian cuisine, fermented castor bean paste becomes the spice ogiri, used to flavour soups. Making it requires careful detoxification of the beans.

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