(Ricinus comes from Latin for a tick, which the seed resembles. Bedbugs last week, ticks today. Communis means common.) CLICK FOR TICK
Euphorbiaceae (the Spurge Family) Misnomer alert: Castorbeans are related to poinsettias, and are not beans.
John and I have been working on a weed project, so today a weed. Although native to the Old Word, castorbean has made itself at home in Florida and far beyond. It’s big, booming, and blooming. A good day to explore a storied history.
Beavers and Castrol
First, how castorbean got its name. Beavers are of the genus Castor, and they make oil. The oil from the plant resembles beaver oil in ways I couldn’t attest to from personal experience. I do have experience with Castrol Motor Oil, however, which owes its name to the “bean,” and thus ultimately to the furry dam builders. Castor oil has unique properties and an esteemed history in engine mechanics, from big airplanes to hobby micro-engines used on model planes, cars, and boats.
Most readers know castor oil not from lubricating their engines, but rather lubricating their innards. It is a laxative, once thought to be a cure-all applied liberally to children, and is famous for its distasteful taste. One curative application was probably against goldbricking. “Oh, you’re too ill to go to school, then you need a big whopping spoonful of castor oil.”
The Fascist Regime in Italy during WWII era likewise prescribed mega doses of castor oil for punishment and for coercion. “We have ways to make you talk, although we may chat in the bathroom.” Not nice, but beats the firing squad. Castor oil as medicine extends back into antiquity.
If you think castor oil is severe, how about ricin? Ricin got in the news as a potential WMD in the hands of terrorists. It was also in the hands of the U.S. Military during WWI, when the American University in Washington DC became the epicenter of grim research. Ricin got a look there for coating bullets and for powdering into a lethal cloud, but research showed it not to work well, despite one researcher getting a fatal snootful. It got another look and another rejection as ineffective during WWII. Therefore I doubt we have to fear it from terrorists, although the lethal protein experienced minor application in spy vs. spy, and somebody mailed some to President Obama. The way ricin kills is interesting…it deactivates ribosomes.
Now, if you did not just complete Biology class, it may be helpful to say ribosomes are where proteins are made. No ribosomes, no proteins, no life. What a great self-defense plan for a plant, because every living thing has ribosomes. Even so, plans and outcomes can differ. Castorbean plants today were acreep with pesky bugs, and with ants.
Castorbean has another line of defense…ants. The plants have glands everywhere, including where leaves join the stem, and on the leaf petioles and blades. The glands feed ants, and the ants presumably protect.
This demonstration of ants on castorbean yesterday takes roughly one minute CLICK
Ants may have another interest in the species. The seed when fresh has a pair of large globular outgrowths on one end. The double doohickey is called the caruncle. Whatever does it do?
Traditionally fleshy seed add-ons are interpretable as ant food, elaiosomes they call em’. The ants grab the food body and relocate the seed, perhaps to their nice protective, aerated, fertilized nest. These hefty castor seeds look like challenging luggage for the average ant. Maybe the caruncle attracts above-average ants or larger critters, even rodents, to drag it. Probably. After all, ants are mighty, and there is teamwork. The plant is native to the Old World Tropics where there are ample ants.
Does the seed look to a bird like a tasty tick, especially with the caruncle as the tick’s head? Can’t rule it out offhand, although consuming the seed contents and not merely the caruncle would release ricin. Biology is full or creatures that have overcome victim defenses. Still, the seeds seem large to pass through a bird undigested, and consuming the flesh of the seed would not merely release the poison but also probably damage the embryo fatally.
Conversely, could the seed surface pattern be warning coloration: “eat me and I’ll wreck your ribosomes?” The pattern on the seed resembles warning colors on noxious arthropods, patterned stinkbugs for instance.
To make it more confusing, some research shows an intact caruncle to improve germination, helping with the seed’s water relations, although the scant relevant publications are not all in accord.
In any case, looking at old seed pods today, the caruncles are gone from the aging but otherwise perfect-looking seeds, and the surrounding pods are loaded with gross buggy manure and occasional wiggling larvae indicted on circumstantial evidence as caruncle snitchers. They limit their mischief to the caruncles and maybe to the surrounding fruit walls, leaving the ricin-laced seed in mint condition. Finding an intact caruncle required opening a fresh new fruit.
The flowers are separate male and female, monoecious in the language of botany, with the females on the stalk above the males. The females have big flesh-colored stigmas; the males look like paintbrushes of pollen.
How do they exchange pollen? Observers generally agree on wind-pollination, especially given the absence of nectar and of apparent petals, and considering the light fluffiness of the abundant pollen, as well as the attribution of allergies to airborne Ricinus pollen. The female flowers look like sea anemones with long tentacles to catch the pollen off of the breeze.
What about insect help? Bee visitation is documented, remembering that bees collect pollen, and might then contact those big overarching stigmas. The lurid meat color of those big fingery stigmas may help replace the petals as attractants, although red is not a bee-favored color. In any event I’ve seen photos of bees on the flowers, so this might be a case of a species able to use wind and insects.
Not many plants out there with more going on than castorbean, from Castrol oil to parental instrument of cure to Fascist instrument of torture to spy’s instrument of silent murder, and all the while rewarding ants from golden cups of nectar. As you walk by, stop and see what insects are visiting the flowers (and send me an e-mail). ((Really))
Abstract re. caruncle: