Plant Talk 7 Botany In a Day Online Class Poisonous Plants

July 21, 2011

Plant Talk 7

Hello plant enthusiasts!

What a whirlwind it has been lately. i have gone from botanizing the hot dry golden hills of California to the cold snow covered grounds of the Cascades in Washington into the Hot and muggy Midwest around St Louis, MO and now find myself back in southern Appalachia around Asheville, NC.

i mentioned a bit about California botany in the last class so in the interest of time and space we will move onto Oregon/Washington. This year i was privileged to attend my 10th National Rainbow gathering  The gathering is held in a national forest in a different state each year. This year’s gathering was in Gifford Pinchot National Forest Southern Washington region near Mt. Saint Helens and Portland, OR.

Humbling….Apparently, they got 150-200% of the normal snow fall last winter and we were greeted upon arrival with 3-4 foot standing snow drifts and cold rain for the first few days!!! Luckily it eventually dried out a bit. The rate of plant development under such circumstance is amazing. We saw quite a change in just over a week of observation. It was like going 3-4 months back in time from what i am used to. Re-experiencing the bloom of Trilliums (Trillium) and Violets (Viola) once again for instance. All in all we took note of over 70 plants in our time there. Medicinals of note included a relative of the Pasque Flower (Anemone oregana) and a type of Osha (Ligusticum) probably species grayii. A common major poisonous plant was the False Hellebore (Veratrum). Major wild edibles included Pioneer Violets (Viola glabella) Marsh Violet (Viola palustris) and Cammas (Camassia). A whole story exists around the Cammas as a major source of food for the natives there and the Death Cammas (Zigadenus venenosus). The Death Cammas bulbs look similar but have a different flower and obviously different effect physiologically. The main common guide book is from the awesome Canadian company Lone Pine (J. Pojar, 2004). Other books i used included the Wildflowers guide from the Audubon Society (Spellenberg, 1979)  and Western Medicinal Plants from the Peterson field guide series (Foster & Hobbs, 2002). The classic flora for the area was written by Gleason and Cronquist (2003) though 7 Song is more fond of a new flora written by Kozolov.

After the Washington Rainbow gathering it took incredible effort to make my way to Botany 2011 in St Louis Missouri. This year’s theme was “Healing the Planet”. A multitude of botanical scientists from all over the world were in attendance! Four societies met in conjunction including the Botanical Society of America, The American Society of Plant Taxonomists, The Fern Society, and the Society for Economic Botany. i feasted on a multitude of classes mainly grouped around Ethnobotany, taxonomy, and teaching methodology. i also got to spend time with all-time heroes like Dr. Peter Raven, Dr. Mary Eubanks, Dr. Michael Balick, Dr. Will McClatchey, and Dr. Sunshine Brosi. The conference was held close to the internationally renowned Missouri Botanical Gardens affectionately and reverently known as MOBOT for short . MOBOT taught me some new plants as all good botanical gardens do and they had a special tree house exhibition too!

i literally drove straight from Botany 2011 to teach at the Firefly Gathering the next day. Firefly really holds a special place in my heart! Earnest, skilled and passionate hard working people convene for workshops with over 80 instructors and 240 classes! Most of the focus is on practical skills from an ancient arts perspective.  If “modern” society ever did crash these are the types of folks i want to be kicking it with. The fun has continued with a intimate more focused group of people taking a range of four intensives including Ethnobotany, Basket making, Forging and Pottery. The one i am affiliated with is for Ethnobotany and guaranteed to be a good time. Natalie Bogwalker, Robin Allison, Sandi Ford, Alan Muskat, Dr. Jim Veteto and myself are taking turns sharing knowledge with a small but highly motivated group of individuals. We have started a plant inventory for the land and found some interesting plants already. Some examples include Carolina Sweet Shrub (Calycanthus), Devils Walking Stick (Aralia spinosa) and Pink Ladies Slippers (Cypripedium acaule). In all, over 100 species have been identified and over half of those are woody plants. We have also found 30 types of mushrooms as well including many edibles like Chanterelles and a Lactarius volemus.

Gatherings will continue for me post firefly through at least two maybe three more wondrous events in Western North Carolina (WNC). Check out the events page for more details.

Poisonous Plants

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 sp.). 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 plants 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 and 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), 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 the authors 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 August 5th

Below are items to think about/comment on. Please write me directly at 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.

-          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.

Thanks, marc

Literature Cited

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.

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