Sunday, September 2, 2018

Edible Plants--Conflicting Stories

elderberry, Sambucus, in flower
elderberry, Sambucus, with unripe berries
Finding out whether a plant you want to gather and eat is safe to eat can be confusing. For some plants, you can quickly find sources that say both "yes it is poisonous" and others that say the exact opposite, "no, it isn't poisonous." Two examples are black nightshade (Solanum nigrum, tomato family Solanaceae) and elderberries (Sambucus spp., elderberry family, Adoxaceae). Both are described on the internet as both edible and poisonous. (Solanum examples: link link link) (Elderberry examples link link link)

a nghtshade, Solanum
a nightshade, Solanum species
Three issues underlie these contradictions: 1) cautious publications, 2) geographical variation with sloppy identification and 3) quantity.

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.
beet tops
Beet tops
Toxic if grown on nitrate-contaminated soil.
2) Geographical variation, species complexes and making assumptions.

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)

pokeweed, Phytolacca americana
pokeweed, Phytolacca americana
Even in the same location, though, individual plants can be less or more toxic than other members of their species growing close by. Growing conditions affect plant chemistry, including small-scale variations in environment. Just as drought-stressed plants are often yellower or redder than plants with adequate water, stressed plants may be higher (or lower) in toxic chemicals.

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 americanumSolanum 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.
Solanum sp.
Its a Solanum, but which one? (Naoshima Island, Japan)
This brings us to "its a big, diverse world." The settlers in the U.S. came from Europe and had European prejudices about which plants they could safely eat. Some of those prejudices changed as they tried American plants, but perhaps some remain. Solanum fruits that look like cherry tomatoes are poisonous in Europe (Solanum dulcamara link) and edible in the Americas (Solanum lycopersicum var. cerasiforme link). Likewise, people from the eastern United States settled the midwest, the Rocky Mountains and the Far West. By the time you get to the Rockies, it is quite a different ecosystem, with very few of the same species that occur in New York or Virginia. What is edible or not in the East is not necessarily the same in the West. Eastern acorns (Quercus) need complex preparation to be safe to eat. Western acorns were a staple of Native American diets because they are much less toxic. Preconceived ideas about plant safety traveled with the people.
California oaks
California oaks
Plants vary a lot over a continent and people often do not realize that. A quick look at the USDA plants data base will show you dozens of species in most groups (genera). Most people are not conscious about how many different species of, say, wild lettuce (Lactuca, sunflower family, Asteraceae link) or goosefoot/wild spinach (Chenopodium, goosefoot family, Chenopodiaceae link) grow in their home state, let alone across the country. So, assuming there's just one "wild lettuce" people are sloppy about determining exactly what they are eating. Accurate identification is hard work. But if you assume that what looks like "the plant from home" is the same plant, when it is not, it is easy for the "same" plant to be both edible and poisonous.

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.

common milkweed, Asclepias syriaca
common milkweed, Asclepias syriaca
Contains toxins used by monarch butterflies
but is also called edible link
On the other hand, books that talk about toxicity from a chemical standpoint do not necessarily discuss whether it is present in 1 part per million or 1,000 parts per million. Often for them, if that molecule causes harm in any dosage and is present, the plant is toxic. And yet, you can safely eat some really nasty molecules if all you take in is 1 or 2 parts per million per day. (Aflatoxins in peanut butter. for example link 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.

small pokeweed plant, Phytolacca americana
small pokeweed plant, Phytolacca americana

In summary:

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.

dandelion, Taraxacum officinale
dandelion, Taraxacum officinale
It IS complicated. Plant species that are both poisonous and safe to eat are real but the explanations in each case may be different. That's one of the things that makes studying plants rewarding for a lifetime. Enjoy the experience--and the flavors.

Comments and corrections welcome.

References and further reading
See links within the post. 
Deane, G. 2007-2018. Eat the weeds.
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)
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)
And 43 years as a plant ecological geneticist, the people who study plant variation in relation to ecology.

Kathy Keeler, A Wandering Botanist

1 comment:

  1. 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?