2015 Plant Talk 8 Poisonous Plants




To the right, an example from one of the most deadly poisonous genera in the world .


(Aconitum lycoctonum)

Hello Plant Enthusiasts!

        We just finished another Firefly Gathering here around Asheville, NC. Firefly really holds a special place in my heart! Over 800 earnest, skilled and passionate hard working people convened for workshops with over 100 instructors and 300 classes! The main focus is on practical skills from an ancient arts perspective.  i lead a plant walk on the ethnobotany of trees, shrubs and vines 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 hanging out with.

        Before that it was my My 40th birthday and visit by parents over the Summer Solstice/Father’s Day weekend… We visited the Outer Banks,. Roanoke Island, Kitty Hawk, Kill Devil Hills, Bodie, and Cape Hatteras. Compiled a nice little list of resources for the botany out there (Club, 1980; Duncan & Duncan, 1987; Hall, 1993; Kraus, 1988; Neyland, 2009; Silberhorn, 1999; Stuckey & Gould, 2001; Tiner, 1993). Bartan Bowers was a local botanist in particular in that area who has an array of botanically related materials in the state archives as well.

        i have felt like i have been in time out for the last week or so. After going practically non-stop for the last two months my get up and go kinda got up and went…Particularly little time or energy for computer related tasks to boot. Major pile up on the internet highway for me...Humbling but after some good rest it feels like my motivation is coming around again…Lots of emotions to deal with that can be messy and challenging too. You can see some of what i mean from my post at the end of Father's Day/Solstice…One step at a time…

        The end of summer solstice and father's day 2015...Celebrating the solstice especially a few days after my birthday is easy...Father's day complicated to be sure....Considering my dad kidnapped me from my mom when i was a year and a half, and i her only child, did not see her again until i was 13...Grew up in a hella abusive household and i am simply thankful on this day that i can honestly say i love him anyway...The only biological father i will ever get and one very different now than the man he used to be , even though still occasionally verbally rough on me...Even more thankful for the stellar man Gerrit Jan Kool, my Pa, that my Mama found subsequently. Who after over 30 years of loving her is such an inspiration to me... We three had a sweet day together...First time at the Outer Banks i hope to remember forever...All you great fathers out there, be they biological or otherwise keep on shining...God bless and hope for redress for the challenging ones too...Such a mixed up time i know for many of you...For the amazing papas passed away, you are with us especially this day...Grateful for all the incredible fathers i know...Praying for all ill will to go...On the longest day of the year, feeling abundantly clear, so many people far and near...love, marc

        There are many more events in July and early August around the Asheville area to come so check out the events page for more details if interested. http://www.botanyeveryday.com/events.

What’s Blooming

        Lately, i have noticed Crepe myrtle (Lagerstroemia indica), Butterfly bush (Buddleja sp.), Butterfly Weed (Asclepias syriaca), Abelia (Abelia sp.), Gooseneck Loosestrife (Lysimachia clethroides), Rose of Sharon (Hibiscus syriacus), Mimosa (Albizzia julibrissin), Phlox (Phlox spp.), Bee Balm (Monarda spp.) and Day Lily (Hemerocallis fulva). Day lily and Rose of Sharon have choice edible flowers for this time of year. Mimosa is an exotic invasive but also anti-depressant. What’s blooming around you?

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.). Frank Cook would speak to referring to this plant as sister ivy or sister oak considering the term poison to be pejorative and provocative towards the plant thus potentially even inciting more ire. Either way this is one to be aware of as is the fact that the toxin manifests as an allergy by which only some people are affected. Those familiar with areas where Mangoes, Brazilian Pepper and Cashews grow will know of potential severe allergic reactions to these foods as well. Interestingly the non-poisonous red fruited Sumacs (Rhus glabra, R. typhina and others) share the same family but widely distributed culinary use all over the temperate world and no toxicity that i know of.

Interestingly the pulp around the seeds of the rather unrelated Gingko has a similar compound to the urushiol in Toxicodendron spp. However, the seed inside of the Gingko is considered a delicacy when cooked. Clearly a class 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. For instance many plants formerly in the Lily family are now placed in the Melanthiaceae and Convallariaceae and both new families contain deadly poisonous members. However, 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 due to furonocoumarins as well including Celery (Apium graveolens) Cow Parsnip (Heracleum sp.) and regular Parsnip (Pastinaca sativa).

The Mint family (Lamiaceae) is probably one of the safest groups 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 (pugelone) and should possibly be avoided during pregnancy. It would be good of course to review all items one might potentially ingest during pregnancy with a special lens…

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.), Poke (Phytolacca americana) 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 a practice in one way labeled bioethnopharmacognosy. However, this is not a very dependable and fail proof 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 2014, p. 219) has a great write 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 is 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. One method of preparation is through boiling or blanching as the acid goes into the water. 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. However, researcher Dr. John Kallas debates the role of oxalic acid in causing health issues in people (Kallas, 2010).

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) which now includes the formerly distinct Milkweed family (Asclepiadaceae) 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 and Orobanchaceae families. Hedge Hyssop (Gratiola) is an outlier from the Lamiaceae that also contains cardiac glycocides.

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). A form of cyanide has also been reported in  the exotic invasive Garlic Mustard (Alliaria petiolata) from the Brassicaceae (Cipollini & Gruner, 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. Elpel includes Lychnis (Caryophyllaceae), Symphoricarpos (Caprifoliaceae) and Cyclamen (Primulaceae) as containing saponins too (Elpel, 2013).

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 Chenopodiaceae, Asteraceae, Poaceae, Brassicaceae and Solanaceae. 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. More can be seen on this in the class covering Phytoremediation.

Plant Poisons That Can Act Topically

        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 & 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 especially important by me are included below.

Trumpet Creeper (Campsis radicans) Bignoniaceae

Spurge (Euphorbia spp.) Euphorbiaceae

Giant Hogweed (Heracleum mantegazzianum) Apiaceae

Wood Nettle (Laportea canadensis) Urticaceae

Stinging Nettle (Urtica dioica) Urticaceae

Posion Ivy/Oak/Sumac (Toxicodendron spp.) Anacardiaceae

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, teacher legendary ethnobotanist Jim Duke at a Warren Wilson College herbal symposium in 2009.

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, Asteraceae, 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 (Claviceps spp.) is a commonly occurring toxic fungus on members of the Poaceae (Elpel, 2013). Aflotoxin is a commonly occurring fungus on several kinds of nuts. A number of books deal with the toxins of plants also cover fungus as well (Blackwell, 1990; Kingsbury, 1964; Turner & Szczawinski, 1995).

Miscellaneous toxic plants

        Many other potentially toxic plants that have not been mentioned occur in temperate regions. Horsetail (Equisetum spp.) Equisetaceae, 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) Annonaceae, 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 many 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. Easy to attain books concerning poisonous effects of plants on humans solely can be referenced for further study on that subject (Alber & 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 specifically the poisonous plants of the eastern U.S. (Blackwell, 1990; Pammel, 1911; 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, 1980). The major families by far followed by number of species listed were the Pea (Fabaceae) (9), Heath (Ericaceae) (8), and Aster (Asteraceae) (6).

Two versions of a classic comprehensive text cover the whole United States (Burrows & Tyrl, 2001, 2013). Regional texts are also available for California (Fuller & McClintock, 1987), Great Britain (Gillam, 2008) and South Africa (Wyk, Heerden, & Oudtshoorn, 2002) respectively.

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 18th

Below are items to think about/comment on. Please write me directly at marc@botanyeveryday.com or leave information in the commentary under this class.


- 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  www.plants.usda.gov       

- 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, commentarially, 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. Englewood Cliffs, NJ: Prentice Hall.

Burrows, G. E., & Tyrl, R. J. (2001). Toxic Plants of North America. Ames, IA: Iowa State University Press.

Burrows, G. E., & Tyrl, R. J. (2013). Toxic Plants of North America (2 edition). Hoboken: Wiley-Blackwell.

Cipollini, D., & Gruner, B. (2007). Cyanide in the chemical arsenal of garlic mustard, Alliaria petiolata. Journal of Chemical Ecology, 33(1), 85–94. http://doi.org/10.1007/s10886-006-9205-x

Club, D. of D. G. (1980). Wild Flowers of the Outer Banks: Kitty Hawk to Hatteras. Chapel Hill: The University of North Carolina Press.

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.

Duncan, W. H., & Duncan, M. B. (1987). The Smithsonian Guide to Seaside Plants of the Gulf and Atlantic Coasts: from Louisiana to Massachusetts, Exclusive of Lower Peninsular Florida. Smithsonian Institution Press.

Elpel, T. (2013). Botany in a Day: The Patterns Method of Plant Identification. Pony, MT: HOPS Press, LLC.

Frohne, D., & Pfander, H. J. (2005). Poisonous Plants: A Handbook for Doctors, Pharmacists, Toxicologists, Biologists and Veterinarians (2nd ed.). Portland, OR: Timber Press, Inc.

Fuller, T. C., & McClintock, E. (1987). Poisonous Plants of California. Berkeley: University of California Press.

Gillam, F. (2008). Poisonous plants in Great Britain. Butleigh: Wooden.

Hall, D. W. (1993). Illustrated Plants of Florida and the Coastal Plain. Gainesville, FL: Maupin House Pub.

Hardin, J. W., & Arena, J. M. (1974). Human Poisoning from Native and Cultivated Plants (2nd ed). Durham, NC: Duke University Press.

Kallas, J. (2010). Edible Wild Plants: Wild Foods From Dirt To Plate. Gibbs Smith.

Kates, A. H., Davis, D. E., McCormack, J., & Miller, J. F. (1980). 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.

Kraus, E. J. W. (1988). A Guide to Ocean Dune Plants Common to North Carolina. (S. Friday, Ed.). Chapel Hill, NC: The University of North Carolina Press.

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.

Neyland, R. (2009). Wildflowers of the Coastal Plain: A Field Guide. Baton Rouge, LA: Louisiana State University Press.

Pammel, L. H. (1911). A Manual of Poisonous Plants. Chiefly of Eastern North America. Cedar Rapids, IA: The Torch Press.

Silberhorn, G. M. (1999). Common Plants of the Mid-Atlantic Coast: A Field Guide (Revised). The Johns Hopkins University Press.

Stuckey, I. H., & Gould, L. L. (2001). Coastal Plants from Cape Cod to Cape Canaveral. Chapel Hill: The University of North Carolina Press.

Tiner, R. W., Jr. (1993). Se Coastal Wetlands Guide (1st ed.). University of Massachusetts Press.

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.

Wyk, B.-E. van, Heerden, F. van, & Oudtshoorn, B. van. (2002). Poisonous Plants of South Africa. Briza.



comments powered by Disqus