June 28, 2011
Plant Talk 7 Poisonous Plants
Hello plant enthusiasts!
What a whirlwind it has been lately. i have gone from botanizing the tundras, taigas, botanical gardens and meadows of Alaska to gardens and farms of the Midwest from Minnesota through Kentucky and now find myself back in southern Appalachia around Asheville, NC. i will be forever grateful to my dear friend Rob Routhieaux for facilitating and largely covering the cost of our trip to Alaska. It was the 50th state visited for both of us and one of the best birthday presents ever! i hope to do a full write up of our adventures and the botany of Alaska sometime in the next few weeks. Thanks to all others who have donated recently as i currently squeak by financially with important but other non-paying work.
i literally drove almost straight from Minnesota, from where i flew to Alaska with Rob, to teach at the Firefly Gathering (about 1,200 miles in 36 hours). Along the way i stopped at the awesome Eagle Bluff Environmental Educational facility www.eagle-bluff.org the famous Seeds Saver’s Exchange Farm www.seedsavers.org, the Lincoln Memorial Garden www.lincolnmemorialgarden.org and the State Botanical Garden of Kentucky in Lexington www.ca.uky.edu/arboretum. The Seed Saver’s Farm visit was a long held dream. A total highpoint was witnessing the over 500 varieties of apples they have planted to preserve the genetic diversity of my favorite fruit.
Firefly really holds a special place in my heart! www.fireflygathering.org Over 700 earnest, skilled and passionate hard working people convened for workshops with over 100 instructors and 200 classes! Most of the focus was on practical skills from an ancient arts perspective. i lead plant walks on useful exotic invasives, craft plants and also taught a class on soda and mead making. If “modern” society ever did crash these are the types of folks i want to be kicking it with. We added over 20 new species to our plant inventory for the land that now totals over 170! We have also found over 30 types of mushrooms as well including many edibles like Chanterelles and Lactarius volemus mostly thanks to the talents of Alan Muskat www.alanmuskat.com .
i am soon on my way to attend my 11th National Rainbow gathering. See website that follows for details www.welcomehome.org This year the gathering will be in Cherokee national forest outside Johnson City, TN and just a couple hours from Asheville! The gathering is held in a national forest in a different state each year. i have just finished making a customized plant list using an advanced search of the USDA database available at www.plants.usda.gov. The search came up with 1172 total taxa and 433 total genera of clubmoss, ferns, conifers, dicots and monocots. We tend to find 100-200 taxa in our week of botanizing the land of each national. All classes held daily are free! Can’t say enough about the wonder and magic of rainbow gathering energy especially when in the back yard of Asheville, NC
There are many more events in July and early August to come so check out the events page for more details.
Well, onto the lesson for this class. A relatively few poisonous plants are largely responsible for many people’s aversion/fear of nature. For instance Poison Ivy/Sumac/Oak….(Toxicodendron spp.). Therefore, a section concerning the main prevalent poisonous plants and their effects on various biota (forms of life) is in order.
The phenomenon of plant poisons offers an excellent venue to examine plants at the family level. Some families tend to be have a majority of poisonous members such as the Buttercup (Ranunculaceae), Arum (Araceae), Tomato (Solanaceae), Bittersweet (Celastraceae) Euphorb, (Euphorbiaceae) and Lily (Liliaceae) families as classically described. We have already covered the fact that new descriptions for Lily like plants (Lilioid) have broken them into many separate families. Edibility versus poisonousness does seem to trend out along SOME of these new family lines. Even families that tend to be predominantly poisonous have some exceptions especially with proper preparation.
For other families it is not nearly as cut and dry. The Carrot family (Apiaceae) contains a multitude of edible plants. It has many famous well used culinary herbs and spices in particular. Which ones can you think of? However, it also contains some of the most toxic plants in the U.S.A. including the Poison Hemlock (Conium maculatum) and Water Hemlock (Cicuta spp.). Several other members of the Apiaceae can cause skin irritation as well including Cow Parsnip (Heracleum sp.) and regular Parsnip (Pastinaca sativa).
The Mint family (Lamiaceae) is probably one of the safest in the world. However, several members can be toxic in high dosages or in the case of pregnancy including Creeping Charley (Glechoma hederacea), Perilla (Perilla frutescens), Germander (Teucrium spp.) and Pennyroyal (Hedeoma pulegioides) (Duke & Foster, 1999; Frohne & Pfander, 2005; Kingsbury, 1964). i have also heard that the American native Mountain Mint (Pycnanthemum spp.) has a similar compound to Pennyroyal and should therefore also be used sparingly at most during pregnancy.
Big families such as the Aster (Asteraceae) and Bean (Fabaceae) have a broad spectrum of plants. Some are used for food, some for medicine and some are poisonous. Several sources list plants by family which may aid in recognizing these trends (Frohne & Pfander, 2005; Kingsbury, 1964; Muenscher, 1940; Westbrooks & Preacher, 1986). Other books specifically address the interface between plant poisons and drugs (Blackwell, 1990; Wink & Van Wyk, 2008).
A classic statement of toxicology attributed to Paracelsus is that “the difference is the dosage”. Therefore, even some poisonous plants may provide powerful medicines through the right means of extraction and appropriate levels of intake. Mayapple (Podophyllum spp.) and Foxglove (Digitalis spp.) are examples of such a phenomenon. Amount of intake, frequency of use, method of exposure, personal biochemistry and site ecology may all influence the effects of certain plants. The fields of genetics and biochemistry are starting to reveal that plant populations can vary greatly in their phytochemistry on a level within the species. Can you think of some reasons why this might be? Some plants are toxic to livestock but not to humans and vice versa. This phenomenon largely has to do with levels of typical intake and differing digestive regimes. Humans have of course historically learned plant uses from animals which is labeled bioethnopharmacognosy. However, this is not a very safe way to test if something is wholesome for human intake.
Numerous compounds are responsible for the phenomenon of plant poisoning. The most prevalent amongst them are various types of alkaloids. Elpel (2004, p. 203) has a great right up in the back of Botany in a Day on various plant compounds discussed below. Other compounds typically cited include polypeptides, amines, glycocides, oxalates, resins, phytotoxins, minerals and compounds causing photosensitivity (Kingsbury, 1964). Many other plants also contain compounds that don’t fall into the above listing but may still cause health problems i.e. hydroquinone in Cocklebur (Xanthium sp.) and Thiaminase in Bracken Fern (Pteridium aquilinum) (Kingsbury, 1964).
Plants containing pyrrolizidine alkaloids typically are located in the Bean, Borage (Boraginaceae) and Aster families (Nelson, Shih, & Balick, 2007). Knowledge of these compounds is relatively recent. Therefore, traditional internal use of plants such as Comfrey (Symphytum officinale) with has such compounds if now often discouraged.
Oxalates are compounds typically found in the Beet (Chenopodiaceae) Buckwheat (Polygonaceae) and Wood Sorrel (Oxalidaceae) families. Purslane (Portulaca oleracea) in the (Portulacaceae) also contains soluble oxalates. These compounds have the potential to leach calcium from the body if not prepared in the appropriate way. Some individuals are particularly susceptible to the formation of stones made of calcium oxalate as well. Care should be exercised in not consuming excessive amounts of members from these families in a raw form. Plants in the Araceae family contain calcium oxalate crystals that may cause an intense burning sensation upon digestion. Fish Tail palm (Caryota sp.) fruits also contain calcium oxalate crystals as i had to learn the hard way in a botanical gardens once. i was going off the idea espoused by Frank Cook that all palm fruits are edible… Remember that nature is not a fan of absolutes like “all” and “never”. The kernel inside even the Fish Tail is edible apparently once the pulp is removed. However, that pulp can even be caustic topically and should be removed with care.
Important glycocides including goitrogenic substances that may inhibit proper thyroid function are present in some members of the Mustard (Brassicaceae) and Beet (Chenopodiaceae) families. Ranunculin is a glycocide in the Buttercup (Ranunculaceae). Cardiac glycocides are the most powerful and typically found in species from the Lily, Dogbane (Apocynaceae) and Foxglove families (Scrophulariaceae). One side note is that many members of the Scrophs as traditionally described including Foxglove have been moved to the Plantaginaceae family.
Cyanogentic glycocides are primarily present in members of the Grass (Poaceae), Bean (Fabaceae), Mochatel (Adoxaceae) and Rose (Rosaceae) families. Small amounts of cyanide occur in the seeds of many members of the Rose family but are normally not an issue at typical rates of consumption by humans. The potential for poisoning of livestock by consumption of the wilted foliage of wild black cherry (Prunus serotina) is well known (Kingsbury, 1964). Cyanogentic compounds also occur in Hydrangea and Elderberry (Sambucus spp.) (Nelson et al., 2007).
Saponins are toxins that have also been used to make soap. A diverse array of plants from several families contain such compounds. A list according to Kingsbury (1964) follows.
Corn Cockle (Agrostemma githago) and Bouncing bet (Saponaria spp.) (Caryophyllaceae)
Alfalfa (Medicago sativa) and Rattle box (Sesbania spp.) (Fabaceae)
Beech (Fagus grandifolia) (Fagaceae)
English ivy (Hedera helix) (Araliaceae)
Poke weed (Phytolacca americana) Phytolaccaceae
Ceanothus (Rhamnaceae), Clethra (Clethraceae), Aesculus (Sapindaceae) and Yucca (Agavaceae) all have saponins as well.
Poisoning by the mineral uptake of plants is another potential cause for concern. Excessive amounts of copper may be taken up by plants in areas where a Bordeaux fungicide have been applied for many years. Note that Bordeaux is a mixture even employed by organic farmers as well. Also cadmium may be taken up where triple superphosphate has been applied (Kingsbury, 1964). Excessive nitrates may especially be taken up by members of the Amaranth, Lambsquarters, Aster, Grass, Mustard and Tomato families. Out west many plants are known to take up harmful amounts of elements like selenium and one should be especially aware in places with serpentine soils.
Some plants can act topically to cause irritation or photosensitation as mentioned above for the Apiaceae. The photosensitivity can be caused through their effect on the liver including members of the Verbena (Verbenaceae) Pea (Fabaceae) Grass (Poaceae) and Buckwheat (Polygonaceae) families. Notable genera in this regard include Knotweed (Polygonum), Vetch (Vicia), Clover (Trifolium), Oats (Avena), and Verbena (Lippia) (Kingsbury, 1964).
Hardin and Arena (1974) compiled a more comprehensive list of 78 plants that grow in the United States which may cause dermatitis. Those that grow in Appalachia and are considered by me especially important are included below.
Trumpet Creeper (Campsis radicans) Bignoniaceae
Spurge (Euphorbia spp.) Euphorbiaceae
Giant Hogweed (Heracleum mantegazzianum)
Wood Nettle (Laportea canadensis)
Stinging Nettle (Urtica dioica)
Posion Ivy/Oak/Sumac (Toxicodendron spp.)
Both types of Nettles are choice edibles that can be picked with gloves and deactivated by drying or cooking. The sting of Urtica is also considered to be of medicinal value as well (Duke & Foster, 1999) One of my all-time favorite ethnobotanical memories is witnessing Frank Cook “urticate” the aching legs of our friend and teacher Jim Duke at a Warren Wilson College herbal symposium. Another source lists even more plants that can irritate the skin (Nelson et al., 2007). In this reference the sources of phytodermatitis are broken down in five categories: mechanical irritants, chemical irritants, allergens, phototoxins and pseudophytodermatitides. The main culprits are the Araceae, Asteraceace, Apiaceae, and Euphorbiaceae.
Toxins from mushrooms and microbes are beyond the scope of the current discussion. However, a couple fungal organisms that act on plant materials do bear mentioning. Ergot is a commonly occurring toxic fungus on members of the Poaceae. Aflotoxin is a commonly occurring fungus on several kinds of nuts. A number of books that deal with the toxins of plants also cover fungus as well (Blackwell, 1990; Kingsbury, 1964; N. J. Turner & Szczawinski, 1995).
Many other potentially toxic plants that have not been mentioned occur in the Appalachian region. Horsetail (Equisetum spp.) has sometimes been recommended for internal ingestion but may cause upset due to the presence of silica. A small fraction of people are sensitive to Pawpaw (Asimina triloba) either through exposure to the skin or ingestion of the fruit (Kingsbury, 1964). Members of the Ericaceae including Laurels (Kalmia spp.) Pieris (Pieris spp.) and Dog Hobble (Leucothoe spp.) are known to be toxic to livestock. Many Ericaceous plants contain sodium channel inhibitors (Nelson et al., 2007). Poisoning may also occur from the consumption of honey that contains nectar from members of the Ericaceae. However, Doug Elliot (2011) says that honey his bees made from Rhododendron was unusually clear and very bitter thereby precluding ingestion. Carolina Jessamine (Gelsemium sempervirens) in the Loganiaceae is a plant that has been shown to cause toxicity in humans both from flowers and honey containing nectar (Hardin & Arena, 1974).
Some plants that are commonly consumed have poisonous parts. Some examples include Elderberry (Sambucus spp.), Pokeweed (Phytolacca americana), Rhubarb (Rheum sp.) and members of the Solanaceae family. A full treatment of poisonous and edible fruits can be referenced for further clarification (Hardin & Arena, 1974). Food allergies are also common to a subset of people. Plants include Nuts, Soybeans (Glycine max), species in the Rosaceae and gluten containing members of Poaceae such as Wheat, Barley, Rye and Spelt.
One must be careful when analyzing the poisonous potential of plants. The devil is in the details. The poisonous nature of plants is often related to a multitude of factors. The information presented here represents a broad overview simply designed to raise the awareness of potential toxins. Several plants and especially plant families mentioned can represent choice members of a healthy diet. Much toxicological research has also focused on the effect to livestock versus people. It is not possible for me to always differentiate between these two classifications at present. Books concerning poisonous effects of plants on humans solely can be referenced for further study on that subject (J. I. Alber & D. M. Alber, 1993; Hardin & Arena, 1974; Nelson et al., 2007). A treatment of over 1,200 poisonous plants of the world and their relative toxicity may give further insight (Wink & Van Wyk, 2008). A couple of books list separately the poisonous plants of the eastern U.S. (Blackwell, 1990; Westbrooks & Preacher, 1986). A publication detailing the most common plants causing poisoning in the southern United States has also been written listing 56 species and 26 families (Kates, Davis, McCormack, & Miller, 197AD). The major families by far followed by number of species listed were the Pea (Fabaceae) (9), Rhododendron (Ericaceae) (8), and Aster (Asteraceae) (6).
Hopefully this overview has given a sense of some of the toxins out there and the major families containing them.
For the next class we will cover major Invasive families it will be posted around July 13th
Below are items to think about/comment on. Please write me directly at email@example.com or leave information in the commentary under this class. Save your comment before submitting if possible as sometimes our spam filter seems to reject them. The problem seems to be connected to how much time you take to submit. I WOULD REALLY LOVE TO HEAR WHAT YOU HAVE TO SAY!!!
- Make a list of the poisonous plants around you and share that info with some people.
- Attend a workshop or a class and write up a brief description of plants or information learned.
- Try to make a list of the plants for your county using the USDA website search at
- Post any clear photos of question plants to Facebook or send in an email.
Praises to all that have donated to the cause. i encourage everyone reading this to donate as they are able financially, commentarialy, or energetically... Your contributions greatly help me continue this crucial work of ethnobotanical research and education. Please let me know your thoughts in general and anyway i can help this class serve you best.
Alber, J. I., & Alber, D. M. (1993). Baby-Safe Houseplants & Cut Flowers: A Guide to Keeping Children and Plants Safely Under the Same Roof. Pownal, VT.: Storey Books.
Blackwell, W. H. (1990). Poisonous and Medicinal Plants. Prentice Hall advanced reference series. Englewood Cliffs, NJ: Prentice Hall.
Duke, J. A., & Foster, S. (1999). A Field Guide to Medicinal Plants and Herbs: Of Eastern and Central North America (Peterson Field Guides) (1st ed.). New York: Houghton Mifflin.
Elliott, D. B. (2011, July 16). Weeds and Woodslore. Presented at the Firefly Gathering, Camp Pinnacle.
Elpel, T. J. (2004). Botany in a Day: The Patterns Method of Plant Identification (5th ed.). Pony, MT: HOPS Press.
Foster, S., & Hobbs, C. (2002). A Field Guide to Western Medicinal Plants and Herbs. Peterson field guide series; Boston: Houghton Mifflin Co.
Frohne, D., & Pfander, H. J. (2005). Poisonous Plants: A Handbook for Doctors, Pharmacists, Toxicologists, Biologists and Veterinarians (2nd ed.). Portland, OR: Timber Press, Inc.
Hardin, J. W., & Arena, J. M. (1974). Human Poisoning from Native and Cultivated Plants (2nd ed.). Durham, NC: Duke University Press.
Hitchcock, C. L., & Cronquist, A. (2003). Flora of the Pacific Northwest: An Illustrated Manual. University of Washington Press.
Kates, A. H., Davis, D. E., McCormack, J., & Miller, J. F. (197AD). Poisonous Plants of the Southern United States. Raleigh, NC: North Carolina Agricultural Extension Service, North Carolina State University.
Kingsbury, J. M. (1964). Poisonous Plants of the United States and Canada. Englewood Cliffs, NJ: Prentice-Hall.
Muenscher, W. C. (1940). Poisonous Plants of the United States. New York: MacMillan Publishing Co.
Nelson, L. S., Shih, R. D., & Balick, M. J. (2007). Handbook of Poisonous and Injurious Plants (2nd ed.). New York: Springer.
Pojar, J. (2004). Plants Of The Pacific Northwest Coast: Washington, Oregon, British Columbia & Alaska (Revised.). Vancouver, Canada: Lone Pine Publishing.
Spellenberg, R. (1979). The National Audubon Society Field Guide to North American Wildflowers: Western Region (1st ed.). Alfred A. Knopf.
Turner, N. J., & Szczawinski, A. F. (1995). Common Poisonous Plants and Mushrooms of North America. Portland, OR: Timber Press.
Westbrooks, R. G., & Preacher, J. W. (1986). Poisonous Plants of Eastern North America (1st ed.). Columbia, SC: University of South Carolina Press.
Wink, M., & Van Wyk, B.-E. (2008). Mind-Altering and Poisonous Plants of the World (1st ed.). Portland, OR: Timber Press.