PLANT OF THE WEEK

Dr. T. Ombrello - UCC Biology Department

 

CASTOR BEAN PLANT

 

 

Common names:        

Castor Bean, Castor Oil Plant, Palma Christi

 

Scientific name      Ricinus communis 

 

Explanation of scientific name:  

Ricinus       – the classical Latin name for this plant.  It is also the Latin name for tick.  The seeds of this plant resemble the bodies of ticks, and Linnaeus used this feature as a basis for the genus name of this plant.

communis  – Latin for common or general.

A Castor Bean plant growing on Union County College's Cranford campus.

The Castor Bean is the only member of the genus Ricinus, and it has no immediate relatives.  As a member of the Spurge family of plants (Euphorbiaceae), it is distantly related to the poinsettia, true rubber tree, cassava, croton, tung oil tree, Chinese tallow tree and crown of thorns.  While the Castor Bean is native only to Africa, people have introduced the species around the world.  It has escaped from cultivation and can be found as a wild and sometimes invasive plant in Australia, many Pacific Islands, and in 27 states (including New Jersey).  In tropical areas it grows as a shrub or a tree that can reach 40 feet in height along streams and rivers and on bottomlands with well-drained, nutrient rich soils.  In temperate areas, Castor Beans are grown as annuals.  In New Jersey they are grown as ornamentals and can be directly sown into gardens in late spring, or started earlier indoors and transplanted outdoors when the weather warms.  Castor Bean plants grow at an amazingly fast rate, if they are situated in full sun and provided with ample fertilizer and water.  Ten-foot tall plants are not uncommon by late summer.  They are intolerant of frost, and die as soon as the temperature drops below  32oF.   

Castor Bean seeds. Castor Bean seedling.
 

 

Castor Bean flowers

and young fruit.

Castor Bean flowers

Male flowers are white.

Female flowers are pink.

(Female: young on left and older on right)

 

Castor Bean plants are impressive.  Their huge, 5 –11 lobed, star-shaped leaves can reach 3 feet in length. The plant’s coarse texture makes a bold statement in a garden, and contrasts nicely with fine textured companions.  They look attractive in groups, or as individual specimen plants.  There are numerous varieties of ornamental Castor Beans.  Many have been selected for bright red or purple foliage, instead of typically green leaves. Leaf shapes and plant size distinguish other varieties.

Castor Bean flowers are relatively inconspicuous.  They lack petals and rely on the wind for pollination.  The flowers are monoecious, meaning there are separate sexed flowers on the same plant.  Flowers are found in terminal clusters, with the male blossoms below and the female blossoms above.  Male flowers senesce shortly after shedding their pollen, while the female flowers develop ˝ -1 inch long capsules covered with soft spines. The capsules open at maturity, revealing 3 smooth, attractive, ˝ inch long seeds that are a mosaic of muted black, gray, brown, yellow-brown, maroon and white colors.  Each seed seems to have its own unique color pattern.  The superficial resemblance of the seeds to a specific species of European tick led to the genus name of the plant.  It is the seeds of Castor Bean plants that have historically, and currently, been of interest. They contain a valuable oil, but also some extremely toxic compounds.

Castor oil makes up about 50% of the weight of the seeds.  The oil is mostly ricinoleic acid, with small amounts of dihydroxystearic, linoleic, oleic, and stearic acids.  It is fast drying, non-yellowing, and is valued for industrial and medicinal purposes.  Most of the world’s production of castor oil goes into lubricants for fine machinery and auto engines, plastics, paints, inks, soaps, linoleum, dyes, leather preservatives, waxes, polishes, cosmetics, candles, and crayons.  Evidence in Egyptian tombs indicates that the oil was used in medicine over 6,000 years ago.  Hundreds of medicinal uses have been claimed over the ensuing years, with purgative, laxative, and general cure all properties cited most frequently.  Ingesting large quantities of the oil can result in poisoning, and many medical professionals feel the oil is a dangerous ingredient in a variety of folk remedies.

After the oil is pressed from the seeds, the remaining “seed cake” can be used as fertilizer or as an animal feed.  For feed use it first must be carefully boiled, heated, or treated by other means to inactivate the toxins present in it.  The toxins in the seeds are water soluble, not lipid (oil) soluble.  So, the toxins remain in the seed cake and are not released during the pressing process.  The crop residues of stems are made into paper and wallboard in some parts of the world.  India is the world’s leader in castor oil production, but commercial production also occurs in California and the southern United States, Australia, Brazil, Venezuela, Morocco, Taiwan, South Africa, Thailand, Haiti, Belgium, Germany, Holland, Peru, China, Argentina, Mexico, Paraguay, Ecuador, and Ethiopia.  Worldwide over 500,000 metric tons of castor oil are produced annually.

Lately, the extremely toxic components of Castor Beans (including the protein ricin and the alkaloid ricinine) have been the subject of much interest.  The most notorious is ricin, a deadly poison found in abundance in the seed and in smaller amounts throughout the rest of the plant.  Ricin is a water-soluble protein that inhibits protein synthesis in animal cells, leading to their death.  Poisoning occurs when animals ingest broken seeds or chew the seeds.  Intact seeds may pass through the digestive tract without releasing ricin.

Ricin is incredibly toxic. As little as 0.5 mg (the amount contained in several seeds) can kill an adult.  One seed can kill a child.  We are not the only sensitive animals.  Four seeds will kill a rabbit, 5 a sheep, 6 an ox or horse, 7 a pig, 11 a dog, but it takes 80 to kill a duck.  Ricin has been investigated for its potential use as an insecticide.

Symptoms of ricin poisoning begin within hours after exposure by ingestion or inhalation.  They include stomach irritation, vomiting, bloody diarrhea, abdominal pain, increased heart rate, low blood pressure, profuse sweating, collapse, convulsions, and death within a few days.  Victims that do not die in 3 to 5 days usually recover.  There is no antidote for ricin poisoning.  The only remedy is to give supportive medical care to minimize symptoms, and hope for the best.  There are some potential medicinal uses for ricin, since it is so cytotoxic.  It might be useful in bone marrow transplant procedures, and as an anti-tumor agent.

There are obvious concerns about the use of ricin as a biological weapon.  What is probably the most well known example of its use as a poison occurred in1978.  Georgi Markov, a Bulgarian dissident who worked for the BBC in London, was murdered as a result of having a 1 mm, ricin-laced pellet stabbed into his leg with a modified umbrella.  The Bulgarian Secret Service was apparently responsible for the assassination.  Other concerns about ricin include reports that it may have been used in the Iran-Iraq war during the 1980’s, and that it has been found in Al Qaeda caves in Afghanistan.

Finally, we grow many plants, both indoors and outdoors, that are poisonous.  In terms of growing Castor Beans as ornamental plants, however, common sense should prevail.  If the flower clusters are removed from the plant as they appear, no seeds will be produced, and the risk of accidental poisoning can be minimized.