I was walking along the edge of the resaca when I noticed a strand of brussels sprouts clinging to the upper stalk of a plant. I did a double take and then high-tailed it to the house for my camera with the long lens – the phone camera not being adequate for this investigation.
The brussels-sprouts-effect was a stem of seed pods at the top of a castor bean plant, Ricinus communis. I’ve always loved the huge, exotic, tropical-looking leaves of this plant. To be honest, I grew one once – not in Texas. I knew the seeds were poisonous, so I cut the tree down in its prime. I don’t recall it blooming. I do remember it became quite large, the stem was thick and tough, and it was a bugger to cut down. I’ve not repeated that venture.
Periodically, I showcase beautiful plants that we don’t want to cultivate – that’s right – we don’t want because, although beautiful, they are invasive plants that can harm the habitat, like castor bean even with its pretty pink, orchid-like blooms and oft-described bizarre seed pods. The showy pink stigmas are the female flowers and the yellow anthers are the male flowers.
Castor bean is native to tropical east Africa around Ethiopia but has naturalized in tropical and subtropical areas around the world. It is considered a weed in many places although it’s grown as an agricultural crop because the beans are valued for their unique oil.
The beans aren’t really beans. Beans, which are also called legumes, are in the Fabaceae family. Castor bean is in the spurge family, Euphorbiaceae. Castor beans are the seeds of the castor bean plant.
Castor bean plants especially love the well-drained banks of receding resacas and irrigation ditches. They are a fast-growing large shrub or small tree that can reach from three to 15 feet tall in a spring-to-summer growing season. The plant has a single stem below and numerous ascending branches above that could do duty as a beach umbrella.
The leaves are spectacular: huge sturdy expanses of starburst green with lovely texture between prominent, ivory colored venation. A leaf can reach 23 inches across; it will have seven to nine deeply toothed, palmlike lobes.
Castor bean were introduced into the United States in the 1800s. The popularity of growing as crops peaked during the 1950s. Components of the oil, known as hydroxy fatty acids, are essential for making high-quality lubricants for heavy equipment or jet engines, according to United States Department of Agriculture’s online AgResearch Magazine. Castor oil also is used in paints, coatings, plastics, antifungal compounds, shampoo and cosmetics; it was a popular medicine in the first half of the 20th century.
Many websites from my Google search touted the castor bean plant as an exotic addition to an ornamental garden. Be cautioned, though. The leaves, and especially the seeds, are highly toxic, they contain a powerful toxic enzyme called ricin. The toxin is seven times more deadly than cobra venom, according to the USDA AgResearch Magazine article. Ricin is toxic to humans, cattle, horses, rabbits, sheep, pigs, goats, gophers, cats, dogs and poultry. Only a few seeds ingested can be fatal to humans. The foliage may cause contact dermatitis when handled; the pollen is toxic to honeybees.
Castor bean plants are classified as noxious weeds in some states and as invasive in others. The rapid growth and thick massive leaves of the plant can shade out native plants. Without abatement, the castor bean will grow in monospecific patches, according to research at the university of Tennessee’s Institute of Agriculture. The plant is particularly harmful to surrounding ecosystems; because of the high ricin concentration in the seed and leaves, the plant can poison local fly, beetle, and ant populations and deposit ricin into river ecosystems.
The Texas Invasive Species website, https://www.texasinvasives.org/ has this to say about the castor bean plant: “While cultivated for its oil, castor bean is noted to exhaust soil. It does not act as a nitrogen fixer. Besides its toxicity, it is noted to cause allergic asthma. It is a heavy seed producer and readily reproduces by seed; seed can remain viable for two to three years and germinate in spring.” A hard frost will kill the plant but not the seeds. (Click the link above to search for invasive species information and how to receive their free monthly newsletter.)
All that said, Baby Boomers may recall a childhood remedy called castor oil, described as “not a gentle” laxative. The oil that is derived from the seeds is a multipurpose vegetable oil that people have used for thousands of years. According to www.healthline.com, the heating process that castor oil undergoes during production deactivates the ricin, making it safe to use. Don't try that at home.
Growing castor bean plants as an ornamental or a crop is not illegal, but extracting and concentrating ricin from it is, which has been compared with potentially making a biological weapon. Under the 1972 Biological Weapons Convention and the 1997 Chemical Weapons Convention, ricin is listed as a schedule 1 controlled substance according to hort.extension.wisc.edu.
It’s interesting to research how and why plants and other species get introduced beyond their native habitats and to learn how things go so terribly awry.
Fortunately, scientists better investigate cause and effect in our generation, but it wasn’t always so.
For instance, while researching the range of the great kiskadee for a recent article, I learned that the birds were introduced to Bermuda. A little back info: great kiskadees are a fairly good-sized bird with a wingspan of 16 inches. They are smaller than a male great-tailed grackle but larger than the female. This is the important part: great kiskadees have a diet scheme commiserate to their physic. They eat a variety of insects like beetles, wasps, grasshoppers, bees and moths. They also will eat small mammals, reptiles, small birds, tadpole and small fish as well as seeds, fruits and berries.
Along with the great kiskadee’s natural range of the Lower Rio Grande Valley south to central Argentina, I’d read that it is very common in Bermuda – because it was introduced in 1957 to control Anolis lizards – because those Jamaican anoles had been brought to Bermuda in 1905 to control fruit flies that were damaging local crops. What a chain of events, right? Granted, great kiskadees are not destructive to the Bermuda habitat.
Quite an opposite outcome happened in some of our southern states. Georgia’s infamous kudzu, Pueraria montana, (which is native to Japan and southeast China) was introduced in 1876 during the Philadelphia Centennial Exposition as a “great ornamental plant for its sweet-smelling blooms and sturdy vines.” During the 1930s, 40s and 50s, it was promoted by the Soil Conservation Service as a way for farmers in the south to control erosion. Sadly, kudzu over-loved the climate of Mississippi, Alabama and Georgia and is now an invasive species that can grow four feet a day and overtake entire forests.