July 25th 2016
Plant Talk 8 Poisonous Plants
Hello Plant Enthusiasts! Witness in this picture one of the most poisonous genera in the world exemplified in this case by the species (Aconitum lycoctonum) known commonly as Monkshood.
What a busy last few weeks! i visited the Berkshire Botanical Gardens, the Botanic Garden at Smith College and Garden in the Woods in Framingham, MA. and have been invited to lecture at Smith by their Horticulture Intstructor and did a plant walk with one of the head gardeners at Garden in the Woods.
i went to the National Rainbow Gathering for the first time in three years and taught several classes with 7 Song and helped establish the Green Path Camp as an educational force along with Mateo Ryall, Dan Farella and Chris Jacobs among others. We all conducted a plant inventory totaling approximately 129 species including some special plants such as Wild Sarsaparilla (Aralia nudicaulis), Bristly Sarsaparilla (Aralia hispida) and Sundew (Drosera rotundifolia). We also found quite a few mushrooms i.e. Red Belted Polypore (Fomitopsis pinicola) Artist’s Conch (Ganoderma applanatum), and the choice edible Aspen Bolete (Leccinum isigne) while making teas daily from fungal and plant based mixtures sourced off the land.
On the way back south i visited the Tower Hill Botanical garden outside of Worcester, MA with Mateo…The best part of that garden for me was the library!
At the invitation of Dr. Ina Vandebroek i made a presentation at the New York Botanical Garden along with friend and colleague Rachel Thomas. My focus was on the Challenges and Opportunities with Exotic Invasive Plants and Rachel’s was on the Herbal Medicine Traditions around her home in Puerto Viejo Costa Rica. Both presentations were well received and i have been invited back and made great contacts for further research.
i also conducted a plant walk for about 15 at Genesis Farm and participated in a memorial ritual to Frank Cook along with the head person in charge sister Miriam and Frank’s friends Jessikah Crouse and David Siller.
The next day was a plant walk at Jim Duke’s legendary Green Farmacy for about 20 people focusing on Food as Medicine. Later that day i spent some good time with Frank Cook's brother Ken. Ken has also gotten into the tradition of leading international trips like his big brother and the next trip will be to Costa Rica! Stay tuned at the previous link for more details as the trip will be next spring.
On my way back down south i also visted Lewis Ginter Botanical Gardens in Richmond, VA. This was voted to be one of the best botanical gardens in the country recently and i was invited to potentially offer a lecture there. The gardens are beautiful to be sure but once again i probably enjoyed the library the most! That said the kids area, and unusual Asian plants were other highlights as well as a display of large lego creations that i have been blessed to also see from Naples Florida to Asheville, NC
Last stop on my way back home i had a great visit with the Executive Director of United Plant Savers (UPS), Susan Leopold. UPS is sponsoring some great Non-Timber Forest workshops in the southeast and Susan has a magical Air BnB set up known as the Trillium Treehouse for anyone travelling along I-66 in Virginia towards Washington D.C.
Upon returning to Asheville, Rachel Thomas taught a couple classes on Traditional Latino Herbalism and Natural Gynecology that i organized at the local community college. Rachel’s website is linked above if you are interested in learning more about her and possibly visiting down in Costa Rica. Meanwhile i have taught several classes on wild edibles with No Taste Like Home through Alan Muskat.
Recently i had am great impromptu meeting with Doug Elliott, Yanna Fishman, Todd Elliott, Jim Veteto, Mycol Stevens, Joe Hollis, and Mateo Ryall to welcome Todd back from Australia and catch up in general. We found lots of interesting mushrooms from the Amanitaceae, Boletaceae and Russulaceae as well as some cool plants like Aconitum and a Platanthera orchid. Their place in general is basically a really cool living history museum and fascinating to take in. Yanna is also a master collector of heirloom varieties of Sweet Potatoes, Beans and other crops. Her work is featured in a publication about Appalachian Place based foods edited by Jim Veteto, Gary Nabhan and others.
Wild Herb Weekend just happened most recently. i taught three classes on Food as Medicine, Native American Ethnobotany and Plants for Love as well as personed a display table where we featured information and goods related to Plants and Healers International. Whew, What a whirlwind!
The 8th annual Green Scene Gathering envisioned by Frank Cook and Ken Crouse will happen7/29 – 7/31. After that i will conduct a Forage and Feast with Holly Drake near Boone, NC on 8/1.
The 23rd annual SE Permaculture Gathering will occur on 8/5 – 8/7 and PHI will have a display table there as well. i will be coordinating all the food and will probably pitching in on a plant/mushroom walk. This event is the first place i distinctly remember bonding with Frank around ethnobotany way back in 2001. The meals are mostly sourced from the local foodshed with a focus on wild components in every meal and classes are arranged using Open Space Technology.
i will also conduct a plant walk with the staff of GAIA Herb Farm on 8/12.
Well, on to 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 of 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 represent widely distributed culinary use all over the temperate world and no toxicity that i know of.
Surprisingly, 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 Lilies (Liliaceae) 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 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/Giant Hogweed (Heracleum spp.) 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 Ale Hoof (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 while pregnant 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 (Azevedo et al., 2001; Binns, Arnason, & Baum, 2002; Boira & Blanquer, 1998; Dhar et al., 2006; Jia & Zhao, 2009; Ogunwenmo, Idowu, Innocent, Esan, & Oyelana, 2007). 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. A number of books look at human poisoning by plants from an historical perspective including how humans can be poisoned by the intake of animal products like milk containing poisonous compounds (Stewart, 2009; Stuart, 2004).
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 amines, glycocides, oxalates, polypeptides, resins, saponins 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 Amaranth (Amaranthaceae) 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 Amaranthaceae 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.
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 Amaranthaceae, 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 photosensitization 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, 2014). One of my all-time favorite ethnobotanical memories is witnessing Frank Cook “urticate” the aching legs of our friend and teacher the 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, 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 (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; N. J. Turner & Szczawinski, 1995; Nancy J Turner & Aderkas, 2009).
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). The Annonaceae also has some pretty severe compounds that may be toxic after extended intake or exposure but at the same time are being researched for use against cancer (He et al., 1997; Levine et al., 2015; McLaughlin, 2008; Pomper, Lowe, Crabtree, & Keller, 2009; Potts et al., 2012; Ye, Alfonso, Evert, & McLaughlin, 1996; Zhao, Miesbauer, Smith, & McLaughlin, 1994).
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 causing allergies include many nuts, Soybeans (Glycine max), species in the Rosaceae and gluten containing members of Poaceae such as Wheat, Barley, Rye and Spelt. I have also met people occasionally with more rare plant allergies such as Cacao, Ginger, Sesame, Nightshades and others…
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; Scott & Thomas, 2000). A treatment of over 1,200 poisonous plants of the world and their relative toxicity may give further insight (Wink & Van Wyk, 2008).
A few 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) Hawaii (Scott & Thomas, 2000) 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 August 6th
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.
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 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.
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