Tim EntwisleCastor Oil Plant’s explosive release of toxic seed

Caster Oil Plant, native to the Eastern Hemisphere, probably Africa, is now a rampant weed in much of the world. In Victoria it is only occasionally established, near gardens from which it escapes, but it extends through a broad strip of southern and eastern Australia.

Castor oil plant, Ricinus communis

Castor oil plant, Ricinus communis

It’s a very successful weed because it grows vigorously in a range of habits, flowers much of the year, produces copious seed after only one year’s growth and that seed is distributed by animals, water, on our shoes and just by itself up to five metres following an explosive release from the capsule.

Ricinus communis belongs to the plant family Euphorbiaceae, most of which have odd flowers. Generally if you can’t work out what family a plant is in, and its flowers are a bit wacky, it’s a euphorb.

Like most euphorbs, Caster Oil Plan has two kinds of flowers, girl ones and boy ones. The boy ones are packed full of branching stalks topped with anthers full of pollen. They look like this:

Ricinus communis castor oil plant male flowers

Ricinus communis castor oil plant male flowers

Ricinus communis male flowers

Ricinus communis male flowers

The girls look almost medieval, like some kind of tiny mace decorated by a fancy red feathered crown. The feathery crown is the style, where the pollen lands to pollinate the flower. The spines are ornamentation, perhaps to ward of predators (and see toxins below).

Ricinus communis female flowers

Ricinus communis female flowers

Ricinus communis female flowers and developing seed pods

Ricinus communis female flowers and developing seed pods

I gather that on the right day you can hear these capsules split, sending seeds ricocheting off the ground, signs and your head. They then look like this.

Ricinus communis open seed pods

Ricinus communis open seed pods

The seed contains Castor Oil, used since at least 4000 BC (based on seeds found in Egyptian tombs) for lamp fuel and god bothering. In generations just a little before mine it was also promulgated as a laxative, even being used in extreme dosage for torture during the Second World War by Italians under the control of Mussolini. Before you rush out to purchase a bottle for personal use, do see below regarding its toxicity.

Cleopatra reputedly used it to whiten her eyes. Again, see below regarding toxicity and note that it reputedly also causes temporary blindness on contact with eyes. In China it has been used for dressing wounds as well as various internal complaints. Again, see below…

By most accounts you must avoid applying the plant to any part of your body, or vice versa. The claim on Missouri Plants website, and many others, is that this plant is ‘more toxic than any other plant to humans’. The culprit is something called Ricin.

Ricin is found throughout the plant, but more so in the seed. This molecule has two parts, one to get it inside an animal cell, the other to replace an essential part (an enzyme) in the pathway to producing protein within a cell. All this means that you die if you consume more than about half a gram of pure ricin if I’ve done my maths correctly.

Castor oil plant Ricinus communis

Castor oil plant Ricinus communis

However it turns out that it is more difficult to be poisoned that it seems. It is extremely emetic, which means if you ingest any you are most likely to vomit it back out again. And the molecules are large and difficult to get into an aerosol, so you are unlikely to inhale it.

Which is all very well but I’d recommend you definitely don’t eat, drink or inhale it. Remember that pests making the mistake of eating the plant usually don’t eat anything again.

[Images: All images from the Reserva Ecológica de Buenos Aires in Argentina, taken when I visited in April this year.
More reading: There are plenty of other potential uses for this plant, in medicine and extracting metals such as Cadmium from soils.]

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Tim Entwisle

About Tim Entwisle

Dr Tim Entwisle is a scientist and scientific communicator with a broad interest in plants, science and gardens, and Director & Chief Executive of Royal Botanic Gardens Victoria. Previously he was Director of Conservation, Living Collections & Estates at Royal Botanic Gardens Kew and prior to that, Director of Sydney’s Royal Botanic Gardens for eight years. Read Tim's full blog at Talking Plants

5 thoughts on “Castor Oil Plant’s explosive release of toxic seed

  1. helen mckerral on said:

    Brings back memories, Tim: there were castor oil plants growing in the street behind the house where I grew up. The seeds themselves are beautiful too: each one is differently marked in cream and brown (if I recall correctly, with some being almost entirely brown, ranging to entirely cream). My grandparents told me the plant was very toxic and to avoid the sap and not to eat any of the seeds, but allowed me to play with them (or perhaps I misremember, and they didn’t know I collected them!). Ricin (or sarin) was the nerve gas used in the Japanese subway attack.

  2. Ada on said:

    Hmmm… Interesting. Where I come from, and about 20 years ago, the standard procedure was to give the women half a glass of Castor oil to drink before admitting them to maternity ward to give birth. It cleaned us out pretty much immediately, so that we didn’t have to inconvenience the doctor by pushing out anything else except the baby….  I don’t think any of us felt poisoned, however.

  3. What doesn’t kill you can only make you stronger? It’s all about quantity of course and most medicines would kill in the right does. As for being careful with kids eating/touching plants, we tend to be a bit blaze but thankfully most of us make it through. That said, this is one I would give to child who put everything they touched into their mouth!

  4. Ian Innes on said:

    It’s a very successful weed because it is a ruderal species – adapted to respond to ground disturbance, high light exposure, high nutrient levels and high concentrations of dissolved salts in the soil profile. It doesn’t persist where those conditions are not available.

  5. The toxicity of ricin is about 1.78 milligrams (!) per average adult, so a tiny speck can kill you (or your child, or dog etc.). It is one of the most toxic poisons on the planet, so plants & seeds need to be handled with great care. This is no joke, but scientifically proven facts.

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