The cockleburs are a rather eccentric genus of weeds in the genus Xanthium, generally unrecognized by most people and cursed by farmers and ranchers. It has a lot going for it, at least in the evolutionary sense. The plants are often ornamented with sharp spines, have spiky burs easily dispersed by animal and human activities, are very toxic, and have invaded much of the globe.
Due to their toxicity they have become a deadly weed in pastures. If consumed by animals they can cause large amounts of death very quickly, and the plant has a habit of growing in large stands and is spread to places animals frequent by the animals themselves. It’s generally not the food of choice for most animals, but less picky animals or animals without other food sources can eat it and become sick or die.
In fact, the genus Xanthium is dangerous enough to have a human bodycount associated with it. Xanthium strumarium has been used as a famine food, mainly because consuming mature foliage in small amounts does not cause immediate symptoms. After massive flooding in Bangladesh nearly 20 people died and 76 were sickened after they ate the plant out of desperation. This is because cockleburs contain carboxyatractyloside, a nasty chemical that resembles the strange and deadly bongkrekic acid in its behavior in the mitochondria. It interferes with the normal movement of ATP and ADP, preventing normal cellular function and energy exchange.
In very small doses this kind of poisoning is not visible nor is it deadly, which is why the plant (unfortunately) has a history of use in traditional Chinese medicine and very limited use as an edible plant. The seeds and seedlings contain much higher levels of carboxyatractyloside than the mature plants, and all parts and stages of the plant contain at least a few other toxins. Slightly larger doses of the plant cause nausea, vomiting, muscle spasms, sweating, breathing issues, heart palpitations, and confusion while larger doses yet can lead to liver failure, seizures, coma, and eventually death. Poisoning that manifests with more severe symptoms has a relatively poor prognosis and symptoms can take a while to manifest if the exposure is chronic.
This is why I was disappointed, though not terribly surprised, to see these plants listed as edible by some sources. Even more worrying is that you can buy the seeds in bulk online (said seeds being promoted as a traditional medicine) and their use in this way has been linked to serious illness and death.
The fact that this plant is still promoted as a food and medicine is inexcusable. The online bible of useful plants, Plants for a Future (PFAF) lists it as edible, even particularly mentioning the seeds and young plants as an edible item before glibly stating that they are probably toxic. As mentioned above, the seeds are possibly the most toxic part of the plant. This is a plant that has many human and animal deaths associated with it, not a choice edible. Perhaps this is why they give it a 1/5 rating for edibility, 0 being inedible and 5 being choice. The problem is that this still implies that the plant is an edible in general.
I don’t think there is much of a case for stating that plants known to be deadly are edible. There are plants regularly eaten by people that require very careful preparation: pokeweed being a great example. The plant can be deadly if eaten raw and is even poisonous to touch without gloves. I think promoting pokeweed as an edible is irresponsible, particularly when there are other, much safer plants that can be used. Pokeweed, at least, has a well-documented history of use and well-understood detoxification strategies. Cockleburs do not – the ethnobotany of the plant is hazier, there isn’t much known about proper preparation of the plant, and cultures that used the plant didn’t seem to use large amounts of it. There is no such thing as informed use of cocklebur other than just not using it.
From the site:
“Leaves and young plants – cooked[2, 105, 177]. They must be thoroughly boiled and then washed[179]. Caution is advised, the plant is probably poisonous[218]. Seed – raw or cooked[212]. It can be used as a piñole[257]. The seed can be ground into a powder and mixed with flour for making bread, cakes etc[105, 257]. The seed contains about 36.7% protein, 38.6% fat, 5.2% ash[179]. It also contains a glycoside[179] and is probably poisonous.”
There should be immediate red flags visible. The plant is not probably poisonous, it is poisonous. The seed is the most dangerous part of the plant, not just ‘probably poisonous’, and should not be used to make anything. By mentioning the plant must be cooked they are (likely unintentionally) implying that the plant is safe to eat after cooking, which I can find no evidence of. They do not make the distinction that young plants are quite dangerous, instead listing them as edible cooked. If you look at the sources, things become weirder. I don’t have access to all of these sources, but I looked at the ones I do:
“[1-2] Dave Jacke, Eric Toensmeier. Edible Forest Gardens. Chelsea Green Publishing Co 2015. ISBN: 9781890132606″
Contains no mention of the genus Xanthium that I can find.
“[179] Reid. B. E. Famine Foods of the Chiu-Huang Pen-ts’ao. Taipei. Southern Materials Centre 1977
A translation of an ancient Chinese book on edible wild foods. Fascinating.”
It’s not a great source. The book was compiled in 1930 and documented plants eaten in times of desperation. Because certain parts of mature Xanthium plants can be consumed in *small* amounts, the fact that some people ate it because they were starving to death does not really convince me that this should even be considered an edible plant. The book also is not a scientific document and shouldn’t have much authority beyond that of a historical document.
“[257] Moerman. D. Native American Ethnobotany Timber Press. Oregon. 1998 ISBN 0-88192-453-9
Very comprehensive but terse guide to the native uses of plants. Excellent bibliography, fully referenced to each plant, giving a pathway to further information. Not for the casual reader.”
Minimal information about quantities eaten or preparation. No mention of toxicity. Little evidence of current use. This is possibly the best source mentioned, but I don’t think the author intends this book as a support for current use of the plants or as a commentary of their safety. Hence why poison oak is listed as an edible and as basket-weaving material.
Deadly Misinformation
I’m not trying to frame PFAF as dishonest or intentionally misleading. I do think they are dangerously naive about how dangerous certain plants are and very sloppy with their sources, a mistake that could have deadly consequences when talking about the edibility of wild plants.
See their entry on poison hemlock, one of the most dangerous plants on earth: edibility score of 1/5, warning that the plant is very dangerous and then telling the reader that the toxin is destroyed by cooking and that there are some edible strains. Their sources for this information?
An online database that does not seem to mention poison hemlock, a 50 year old book from Japan they describe as having many entries that are ‘more than a little dubious’, a field guide to European flowers that also around 50 years old, and a famous permaculture book that does nothing but talk about how dangerous the plant is. Since the permaculture book only mentions the plant as a nectar source to insects and as a plant deadly to humans, and the database doesn’t seem to mention the plant at all, it can only be assumed that PFAF is basing their score of poison hemlock as an edible plant based on a field guide to flowers and a book that is often ‘more than a little dubious’, both around half a century old.
Given that around two oranges worth (300 grams) of poison hemlock is enough to kill an adult cow and 6-8 leaves (~150 mg) can kill a fully-grown human, doesn’t it make sense that they would seek a more credible source before claiming the plant is edible in any capacity? I can find no evidence that the toxins are destroyed fully by cooking, nor can I find any actual evidence of edible strains in the UK. Telling people the plant is edible in any capacity is wildly irresponsible and, in my opinion, misinformation.
Putting this kind of information out on the internet, particularly if it is dressed in ‘sciencey’ sounding language or given a sense of authority by adding lots of citations, is an invitation to tragedy. Somebody might consider PFAF an authoritative source on plant safety, consume a plant, and become ill or worse.
So is Xanthium edible?
Calling Xanthium an edible plant without giving enough information is irresponsible. Xanthium is edible in the sense that motor oil and gravel are edible: there is no benefit of consumption, eating a tiny amount probably won’t’ kill you, and if you eat a bit too much you will probably get very sick and might die. Is that really what we want to call an edible plant?
Xanthium has killed people and unfortunately will probably continue to do so. There is no known safe method of consumption because the plant is not that well understood. The only safe way to eat cocklebur is to not eat it at all, and that doesn’t sound like an edible plant to me and I would be very uncomfortable stating otherwise.