Ricinus communis, the castor bean^[1] or castor oil plant,^[2] is a species of perennial flowering plant in the spurge family, Euphorbiaceae. It is the sole species in the monotypic genus, Ricinus, and subtribe, Ricininae. The evolution of castor and its relation to other species are currently being studied using modern genetic tools.^[3] It reproduces with a mixed pollination system which favors selfing by geitonogamy but at the same time can be an out-crosser by anemophily (wind pollination) or entomophily (insect pollination).^[4]

Its seed is the castor bean, which, despite its name, is not a true bean. Castor is indigenous to the southeastern Mediterranean Basin, Eastern Africa, and India, but is widespread throughout tropical regions (and widely grown elsewhere as an ornamental plant).^[5]

Castor seed is the source of castor oil, which has a wide variety of uses. The seeds contain between 40% and 60% oil that is rich in triglycerides, mainly ricinolein. The seed also contains ricin, a water-soluble toxin, which is also present in lower concentrations throughout the plant.

An unrelated plant species of similar appearance, Fatsia japonica (false castor oil plant), grows in Japan.

Description

Ricinus communis can vary greatly in its growth habit and appearance. The variability has been increased by breeders who have selected a range of cultivars for leaf and flower colours, and for oil production. It is a fast-growing, suckering shrub that can reach the size of a small tree, around 12 m (39 ft), but it is not cold hardy.

The glossy leaves are 15–45 cm (6–18 in) long, long-stalked, alternate and palmate with five to twelve deep lobes with coarsely toothed segments. In some varieties they start off dark reddish purple or bronze when young, gradually changing to a dark green, sometimes with a reddish tinge, as they mature. The leaves of some other varieties are green practically from the start, whereas in yet others a pigment masks the green color of all the chlorophyll-bearing parts, leaves, stems and young fruit, so that they remain a dramatic purple-to-reddish-brown throughout the life of the plant. Plants with the dark leaves can be found growing next to those with green leaves, so there is most likely only a single gene controlling the production of the pigment in some varieties.^[8] The stems and the spherical, spiny seed capsules also vary in pigmentation. The fruit capsules of some varieties are more showy than the flowers.Male flowerFemale flowerThe green capsule dries and splits into three sections, forcibly ejecting seeds

The flowers lack petals and are unisexual (male and female) where both types are borne on the same plant (monoecious) in terminal panicle-like inflorescences of green or, in some varieties, shades of red. The male flowers are numerous, yellowish-green with prominent creamy stamens; the female flowers, borne at the tips of the spikes, lie within the immature spiny capsules, are relatively few in number and have prominent red stigmas.^[9]

The fruit is a spiny, greenish (to reddish-purple) capsule containing large, oval, shiny, bean-like, highly poisonous seeds with variable brownish mottling. Castor seeds have a warty appendage called the caruncle, which is a type of elaiosome. The caruncle promotes the dispersal of the seed by ants (myrmecochory).

Nomenclature

The name Ricinus is a Latin word for tick; the seed is so named because it has markings and a bump at the end that resemble certain ticks. The genus Ricinus ^[6] also exists in zoology, and designates insects (not ticks) which are parasites of birds; this is possible because the names of animals and plants are governed by different nomenclature codes.^{[citation needed]}

The common name “castor oil” probably comes from its use as a replacement for castoreum, a perfume base made from the dried perineal glands of the beaver (castor in Latin).^[7] It has another common name, palm of Christ, or Palma Christi, that derives from castor oil’s reputed ability to heal wounds and cure ailments.

Medicinal uses

Castor oil has many uses in medicine and other applications.

An alcoholic extract of the leaf was shown, in lab rats, to protect the liver from damage from certain poisons.^[10][11][12] Methanolic extracts of the leaves of Ricinus communis were used in antimicrobial testing against eight pathogenic bacteria in rats and showed antimicrobial properties. The pericarp of Ricinus showed central nervous system effects in mice at low doses. At high doses mice quickly died.^[13] A water extract of the root bark showed analgesic activity in rats.^[13] Antihistamine and anti-inflammatory properties were found in ethanolic extract of Ricinus communis root bark.^[14]

Other uses

Extract of Ricinus communis exhibited acaricidal and insecticidal activities against the adult of Haemaphysalis bispinosa Neumann (Acarina: Ixodidae) and hematophagous fly Hippobosca maculata Leach (Diptera: Hippoboscidae).^[15]

Members of the Bodo tribe of Bodoland in Assam, India, use the leaves of this plant to feed and rear the larvae of muga and endi silkworms.

Castor oil is an effective motor lubricant and has been used in internal combustion engines, including those of World War I airplanes, some racing cars and some model airplanes. It has historically been popular for lubricating two-stroke engines due to high resistance to heat compared to petroleum-based oils. It does not mix well with petroleum products, particularly at low temperatures, but mixes better with the methanol-based fuels used in glow model engines. In total-loss-lubrication applications, it tends to leave carbon deposits and varnish within the engine. It has been largely replaced by synthetic oils that are more stable and less toxic.

Jewelry is often made of castor beans, particularly necklaces and bracelets.^[16]

Habitat, growth and horticultural uses

In Greece it is hardy enough to grow as a small tree. In northern countries it is grown instead as an annual.Cotyledons (round) and first true leaves (serrated) on a young plant. This plant is about four weeks old.Young plant

Although Ricinus communis is indigenous to the southeastern Mediterranean Basin, Eastern Africa, and India, today it is widespread throughout tropical regions.^[5] In areas with a suitable climate, castor establishes itself easily where it can become an invasive plant and can often be found on wasteland.

It is also used extensively as a decorative plant in parks and other public areas, particularly as a “dot plant” in traditional bedding schemes. If sown early, under glass, and kept at a temperature of around 20 °C (68 °F) until planted out, the castor oil plant can reach a height of 2–3 metres (6.6–9.8 ft) in a year. In areas prone to frost it is usually shorter, and grown as if it were an annual.^[5] However, it can grow well outdoors in cooler climates, at least in southern England, and the leaves do not appear to suffer frost damage in sheltered spots, where it remains evergreen.^{[citation needed]} It was used in Edwardian times in the parks of Toronto, Ontario, Canada. Although not cultivated there, the plant grows wild in Southern California, notably Griffith Park in Los Angeles.^[17]

Cultivars

Selections have been made by breeders for use as ornamental plants (heights refer to plants grown as annuals) and for commercial production of castor oil.^[9]Ornamental cultivars

• ‘Carmencita’ has gained the Royal Horticultural Society‘s Award of Garden Merit^[18][19]
• ‘Carmencita Bright Red’ has red stems, dark purplish leaves and red seed pods;
• ‘Carmencita Pink’ has green leaves and pink seed pods
• ‘Gibsonii’ has red-tinged leaves with reddish veins and bright scarlet seed pods
• ‘New Zealand Purple’ has plum colored leaves tinged with red, plum colored seed pods turn to red as they ripen(All the above grow to around 1.5 metres (4.9 ft) tall as annuals.)^[5]
• ‘Impala’ is compact (only 1.2 metres or 3.9 feet tall) with reddish foliage and stems, brightest on the young shoots
• ‘Red Spire’ is tall (2–3 metres or 6.6–9.8 feet) with red stems and bronze foliage
• ‘Zanzibarensis’ is also tall (2–3 metres or 6.6–9.8 feet), with large, mid-green leaves (50 centimetres or 20 inches long) that have white midribs^[9]

Cultivars for oil production:

• ‘Hale’ was launched in the 1970s for the State of Texas.^[20] It is short (up to 1.2 m or 3 ft 11 in) and has several racemes
• ‘Brigham’ is a variety with reduced ricin content adapted for Texas. It grows up to 1.8 m (5 ft 11 in) and has 10% of the ricin content of ‘Hale’
• ‘BRS Nordestina’ was developed by Brazil’s Embrapa in 1990 for hand harvest and semi-arid environments
• ‘BRS Energia” was developed by Embrapa in 2004 for mechanised or hand harvest
• ‘GCH6’ was developed by Sardarkrushinagar Dantiwada University, India, 2004: it is resistant to root rot and tolerant to fusarium wilt
• ‘GCH5’ was developed by Sardarkrushinagar Dantiwada University, 1995. It is resistant to fusarium wilt
• ‘Abaro’ was developed by the Ethiopian Institute of Agricultural Research‘s Essential Oils Research Center for hand harvest
• ‘Hiruy’ was developed by the Ethiopian Institute of Agricultural Research’s Melkassa and Wondo Genet Agricultural Research Centers for hand harvest during 2010/2011

Plant-animal interactions

Ricinus communis is the host plant of the common castor butterfly (Ariadne merione), the eri silkmoth (Samia cynthia ricini), and the castor semi-looper moth (Achaea janata). It is also used as a food plant by the larvae of some other species of Lepidoptera, including Hypercompe hambletoni and the nutmeg (Discestra trifolii).

Allergenic potential

Ricinus is extremely allergenic, and has an OPALS allergy scale rating of 10 out of 10. The plant is also a very strong trigger for asthma, and allergies to Ricinus are commonplace and severe.^[21]

The castor oil plant produces abundant amounts of very light pollen, which easily become airborne and can be inhaled into the lungs, triggering allergic reactions. The sap of the plant causes skin rashes. Individuals who are allergic to the plant can also develop rashes from merely touching the leaves, flowers, or seeds. These individuals can also have cross-allergic reactions to latex sap from the related Hevea brasiliensis plant.^[21]

Toxicity

The toxicity of raw castor beans is due to the presence of ricin. Although the lethal dose in adults is considered to be four to eight seeds, reports of actual poisoning are relatively rare.^[22] According to the Guinness World Records, this is the world’s most poisonous common plant.^[23] Symptoms of overdosing on ricin, which can include nausea, diarrhea, tachycardia, hypotension and seizures, persist for up to a week. However, the poison can be extracted from castor by concentrating it with a fairly complicated process similar to that used for extracting cyanide from almonds.

If ricin is ingested, symptoms commonly begin within 2–4 hours, but may be delayed by up to 36 hours. These include a burning sensation in mouth and throat, abdominal pain, purging and bloody diarrhea. Within several days there is severe dehydration, a drop in blood pressure and a decrease in urine. Unless treated, death can be expected to occur within 3–5 days; however, in most cases a full recovery can be made.^[24][25]

Poisoning occurs when animals, including humans, ingest broken castor beans or break the seed by chewing: intact seeds may pass through the digestive tract without releasing the toxin.^[24] The toxin provides the castor oil plant with some degree of natural protection from insect pests such as aphids. Ricin has been investigated for its potential use as an insecticide.^[26] The castor oil plant is also the source for undecylenic acid, a natural fungicide.

Commercially available cold-pressed castor oil is not toxic to humans in normal doses, either internal or externally.^[27]

Chemistry

Three terpenoids and a tocopherol-related compound have been found in the aerial parts of Ricinus. Compounds named (3E,7Z,11E)-19-hydroxycasba-3,7,11-trien-5-one, 6α-hydroxy-10β-methoxy-7α,8α-epoxy-5-oxocasbane-20,10-olide, 15α-hydroxylup-20(29)-en-3-one, and (2R,4aR,8aR)-3,4,4a,8a-tetrahydro-4a-hydroxy-2,6,7,8a-tetramethyl-2-(4,8, 12-trimethyltridecyl)-2H-chromene-5,8-dione were isolated from the methanol extracts of Ricinus communis by chromatographic methods.^[28] Partitioned h-hexane fraction of Ricinus root methanol extract resulted in enrichment of two triterpenes: lupeol and urs-6-ene-3,16-dione (erandone). Crude methanolic extract, enriched n-hexane fraction and isolates at doses 100 mg/kg p.o. exhibited significant (P < 0.001) anti-inflammatory activity in carrageenan-induced hind paw oedema model.^[29]

Modern commercial usage

Global castor seed production is around two million tons per year. Leading producing areas are India (with over three-quarters of the global yield), China and Mozambique, and it is widely grown as a crop in Ethiopia. There are several active breeding programmes.

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