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| elderberry, Sambucus, with unripe berries |
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| a nightshade, Solanum species |
1) People publishing about edibility tend to err in the direction of caution. They don't want anyone to ever say to them "You said it was safe but it made me very sick." Quite apart from legal considerations, that would be an appalling experience. Since people vary a lot in their tolerances, that means there are cautions given even for plants like chamomile (Matricaria chamomilla), a common herbal tea. Chamomile's issue is that it is in the sunflower family, Asteraceae, which means it might set of an allergic reaction in someone intensely allergic to ragweed (Ambrosia spp., also sunflower family).
People publishing also warn you if the plant can concentrate toxins, even if that rarely happens. Agricultural fields are generally free of toxins that plants can pick up from the soil and pass on to the consumer. However, someone foraging in their neighborhood might find otherwise edible plants on contaminated ground. Where we know that a plant will pick up environmental toxins, experts tend to be very cautious and mark it as dangerous. This can seem weird: corn and beets, generally edible, can concentrate enough nitrates to cause nitrate poisoning in people and livestock if growing on nitrate-enriched soil. Wild plants, for example pigweeds (Amaranthus spp.) similarly can be toxic depending on where they grow (link p. 66). Other plants take up specific metals to a dangerous degree, for example selenium or lead. Since it is hard to know where one's readers might encounter a site with absorbable toxins, experts simply warn against eating plants that take up toxins from their environment. If you know the soils where your plants were grown are clean, these plants are clearly edible. But some places they are toxic.
For all these reasons, you can find people eating plants books or websites list as poisonous.
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| Beet tops Toxic if grown on nitrate-contaminated soil. |
Almost every plant that people gather to eat is found in several states or countries. Plants with a limited range don't get much publicity, no matter how tasty they are. However, the plants didn't promise us that their chemistry would be uniform across even moderate distances. Think about how the color of some wildflowers is different in different areas. We usually don't know why. That same kind of variation applies to plant chemistry, including the compounds that make a plant toxic or edible. There's no easy answer for deciding whether or not to eat a plant if it is reported that in some places it is ok and some places it made people or animals sick.
My first advice in this case would be to compare the situations. Did both the eater that said it was delicious and the one who said they were sick all night gather the same plant part (young leaves for example), at the same time of year (spring) and prepare it the same way (as steamed greens). Differences in the plant material gathered might account for the difference. Poke, Phytollaca americana, is famous for being both a poisonous plant and salad green, at least partly because the old leaves are much more toxic than the young leaves. (link)
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| pokeweed, Phytolacca americana |
Where the plant reportedly ranges from delicioius to mildly nauseating, it may be worth trying it. If the toxic end of the spectrum is life-threatening, I personally will avoid that plant except in a famine.
Within-species variation is very real, but probably some of the contradictions about whether plants are edible come not from within-species variation but from variation between difficult to distinguish species. Biologists often call groups of species that are difficult or impossible to tell apart a "species complex." Sometimes plants (or other organisms) are considered a species complex simply because no one has studied the group. (There are far more botanical questions than botanists). Sometimes the species really are indistinguishable to the human eye, differing in important internal chemistry or chromosome arrangement, for example, but not in any shape or color features.
Incomplete knowledge is very dangerous to foragers. When I worked in western Nebraska in the 1970s, Solanum nigrum, black nightshade, was the name given in the authoritative plant identification books for the nightshade that grew on the roadsides. Today, Solanum nigrum is not found in the state of Nebraska at all. It hasn't vanished. Rather, recent study determined that the Nebraska plant was an American native species, Solanum americanum. Solanum nigrum is a European plant and not widespread in North America. Because the books gave me poor information, I inaccurately applied information published about Solanum nigrum to a totally different species.
There are at least 60 species of Solanum you might encounter in North America and many more around the world. They are hard for even experts to tell apart. My take on "nightshade is poisonous" vs "I eat nightshade all the time" is that some nightshades are dangerous and some are not. In this particular case, analysis by experts is overdue. Until then, it doesn't really help to know that it is a mess if you don't know which ones are safe and which aren't. One simple suggestion: if you eat nightshade fruits at home, be wary tasting nightshades in distant locations.
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| Its a Solanum, but which one? (Naoshima Island, Japan) |
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| California oaks |
Plant toxicity varies within species and between similar-looking species.
3) Quantity. My final thought is that many "I eat those berries raw all the time" quotes are from a person who takes six off the plant during a hike every weekend while the person who ended up in the hospital ate a bowl-full for dessert. The quantities of kitchen vegetables and fruits that we eat are generally much greater than the number of berries or leaves we pick tasting wild things.
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| common milkweed, Asclepias syriaca Contains toxins used by monarch butterflies but is also called edible link |
Dosage is crucial. Poison books and authorities say that over and over. Most plant toxins do damage in proportion to the amount you eat.
What that means in a practical sense is: Go cautiously, first a tiny amount, then, carefully larger amounts, when eating a wild plant with a mixed reputation.
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| small pokeweed plant, Phytolacca americana |
Always read about the plant in several places so you know if it was ever called poisonous.
Many published works have and will continue to err on the side of caution.
When using a foraging book or website, spend a few minutes to get sense of the author's level of risk-taking. If the book or site is shot full of warnings, clearly the author is quite cautious and may avoid some good plants. If the author boldly urges you to disregard all the warnings about toxic species, you should be sure that you are in the same region eating the same thing cooked the same way as the author.
Secondly, plants vary, especially over hundreds of miles. Check the foraging book or site to know where the author lives. Is he or she somewhere near you or from halfway across the continent? The chances that the book's advice isn't quite right for you increase with distance.
Finally, with any new food but especially a plant with a mixed reputation, taste a little and wait hours or a day before eating more. Don't make it a major part of the meal until you've eaten it on several occasions. Learn about how to prepare it, just as you did with vegetables from the grocery store. And just as you pay attention to brand name and product details (peaches in heavy syrup versus peaches in water) pay attention to when and where the wild plants were collected to learn what to do again and what to avoid. Wild dandelion greens (Taraxacum officinale sunflower family, Asteraceae), to name an obvious example, are quite tasty in early spring and, to me, unpalatably bitter in midsummer.
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| dandelion, Taraxacum officinale |
Comments and corrections welcome.
References and further reading
See links within the post.
Deane, G. 2007-2018. Eat the weeds. Eattheweeds.com
Harrington, H. D. 1967. Edible Native Plants of the Rocky Mountains. University of New Mexico Press, Albuquerque, New Mexico.
Kallas, J. 2010. Edible Wild Plants. Gibbs and Smith, Layton Utah.
Plants for a Future 1996-2012 (accessed 9/2/18) pfaf.org
Stewart, A. 2009. Wicked Plants. Algonquin Books, Chapel Hill, North Carolina.
Thayer, S. 2006. The Forager's Harvest. Forager's Harvest Press, Birchwood, Wisconsin (and his other books) www.foragersharvest.com
And 43 years as a plant ecological geneticist, the people who study plant variation in relation to ecology.
Kathy Keeler, A Wandering Botanist
More at awanderingbotanist.com
Thank you for creating this blog. I am a scientist and appreciate the scientific way you present plant differentiation criteria. Do you conduct any 'edible plant vs poisonous' courses online?
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