January 28, 2013

Don't Eat That Bean!

After writing recent posts about Poison Sumac and White Snakeroot, I got to thinking more about poisonous plants. Plants can have wondrous healing properties, of course, but there sure are some to be avoided out there. And some can be both good and bad for humans, depending on which part is used and/or how it is prepared. I was reminded about all this on our trip to Florida when we walked by a big thriving stand of one of the most poisonous plants on the planet, Castor Bean (Ricinus communis), at Loxahatchee National Wildlife Refuge:

Those big, palmately-veined leaves are unmistakable.  I remember seeing this plant growing as a weed when I lived in San Diego, and a botanist friend with whom I was birding filled me in on its potent properties. 

Plants, which can't fly, scream or run out of the way of something attacking them, have to have some defense against hungry critters. Chemicals, thorns, leathery texture and other obstacles fill that bill. Often those defenses are inconvenient or even hazardous to humans, but for me they add a lot of interest to the botanical world and Castor Bean is way up there on my list of fascinating plants.

Native to Ethiopia, Castor Bean grows well in many tropical areas and has become a weed in southern parts of the United States. It can be grown in Ohio and other temperate areas from seed as an ornamental annual, although as you'll see that doesn't seem like a great idea even though Amazon, eBay and other sources can fix you right up with seeds. Cultivars are available with purple and red leaves, but the seeds should definitely be kept away from children.

Castor Bean flowers are rather unusual:

They are not very conspicuous, lack petals and are pollinated by wind. Male and female flowers are separate, but the plant has both on a stalk called a raceme. The male flowers are below the female flowers. Here is a closeup of the flowers:

Once pollinated, the female flowers develop spiny capsules which each contain 3 half-inch long speckled seeds. The seeds (which, despite their name, are not really beans; Castor Bean is in the spurge family or Euphorbiaceae, along with poinsettias) can be seen here.

While intact seeds can pass through the digestive tract without causing a problem, if the outer shell is broken or chewed they can cause extremely severe gastrointestinal reactions and can be fatal. These effects are due to a chemical called ricin, which prevents cells from making proteins. Ricin is also present in lesser concentration throughout the plant. In addition, allergenic compounds can be found on the plant's surfaces which can cause nerve damage, making castor bean harvesting a hazardous profession.

Why harvest castor beans? Well, the flip side of the toxicity of these plants is the fact that if you mash up the beans and extract the oil, you have the familiar component of traditional and alternative medicines, castor oil. The process separates the ricin from the oil, since ricin is water soluble and not soluble in oil. The ricin can then be destroyed by heating while processing the leftover mash into fertilizer.

Here are some facts about uses (and misuses) of castor beans, ricin and castor oil--references are at the end.

  • One castor bean seed can kill a child, 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 (statistics which mainly prove that human curiosity has no boundaries...).
  • In addition to potentially fatal gastroenteritis, castor beans can also cause neurological and ophthalmological lesions
  • According to the Centers for Disease Control, in 1978, Georgi Markov, a Bulgarian writer and journalist who was living in London, died after a man stabbed him with an umbrella, which injected a ricin pellet.
  • Castor oil is a good motor lubricant and has been used in internal combustion engines, including those of World War 1 airplanes, some racing cars and some model airplanes. It does not, however, mix with petroleum products. It has been largely replaced by synthetic oils that are more stable and less toxic.
  • Castor oil is used in the food industry as food additives, flavorings, and as a mold inhibitor.
  • The United States Food and Drug Administration has categorized castor oil as a "generally recognized safe and effective" laxative but it can cause painful cramps and can, shall we say, be a much more powerful laxative than is usually needed or desired.
  • In traditional medicine, castor oil has been used for just about everything, from skin problems to birth control, to headaches, muscle aches, and sinusitis. It has been used to induce labor, but the accompanying awful vomiting and diarrhea render it inadvisable for that application.
Here are some interesting links for more information:

The chemical properties of plants continue to be mind-boggling to us humans, who try so hard to understand and explain the world around us. Here is one last photo of a Castor Bean plant, and notice that in all of these photos of mature plants you don't see any insect damage on the leaves--likely for a very good reason! 


  1. I really enjoyed your article. Since ricin has been in the news, I was at least familiar with it. And I had heard that it was derived from the Castor bean. But I had no idea what it looked like. However after looking over your photos, I'm thinking that I've photographed it myself without knowing what it is. The leaves that I photographed had a reddish tint. It's difficult for me to find the photo though. Since I didn't know what it was, I didn't tag it. On the up side, I apparently didn't come in contact with allergenic compounds on the surface of that plant.

    I also enjoyed your post's dry humor, such as "statistics which mainly prove that human curiosity has no boundaries...". LOL

  2. Thanks so much for your note! There are definitely red-leaved cultivars of Castor Bean available--here is a link for some photos: http://deesgardens.com/Castorbean.html