Plant Talk 9 Poisonous Plants
Hello Plant Enthusiasts!
A relatively few poisonous plants are largely responsible for many people’s aversion/fear of nature, e.g. 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 possibly 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.
When covering a subject like the use and possible ingestion of plants clearly a class concerning the main prevalent poisonous plants and their effects on various 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 depending on 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.). Poison Hemlock looks very similar to Queen Anne’s Lace (Daucus carota) and some Biscuitroots (Lomatium spp.) Water Hemlock can look similar to a number of other plants in the family like Angelicas 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, 2014; 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 as well. It would be good of course to review all items one might potentially ingest while pregnant with a special lens towards safety…
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; Schlag & McIntosh, 2006; Searels, Keen, Horton, Clarke, & Ward, 2013). 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) which 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 (2010) debates the role of oxalic acid in causing health issues in people.
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. They are typically found in species from the Lily, Foxglove (Scrophulariaceae) and Dogbane (Apocynaceae) families. The Apocynaceae now includes the formerly distinct Milkweed family (Asclepiadaceae). 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). Steroidal saponins are also used medicinally in plants like Ginseng and Sweet Tea Vine (Gynostemma pentaphylla) (Chang, Chang, Lin, Liu, & Chen, 2005; Cui, Eneroth, & Bruhn, 1999; Razmovski-Naumovski et al., 2005; Schlag & McIntosh, 2006).
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; Stewart, 2009). 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 potentially 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 medicinally but may cause upset due to the presence of silica (Abbe, 1985; Rogers, 2014).
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; G. Zhao, Hui, Rupprecht, McLaughlin, & Wood, 1992; G. X. Zhao, Chao, Zeng, & McLaughlin, 1996; G. X. 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. 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; Dauncey, 2010; Hardin & Arena, 1974; Nelson, Shih, & Balick, 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. A number of books also cover poisonous plants of Florida and the Caribbean as well (Adams, Magnus, & Seaforth, 1963; Dahlgren, 1944; Lowe, Morrison, Magnus, & Campbell-Grizzle, 2004; Morton, 1971; Nellis, 1997).
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 October 3rd
Below are items to think about/comment on. Please write me directly at firstname.lastname@example.org 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.
Abbe, E. M. (1985). The Fern Herbal: Including the Ferns, the Horsetails, and the Club Mosses. Ithaca: Cornell Univ Pr.
Adams, C. D., Magnus, K., & Seaforth, C. (1963). Poisonous Plants in Jamaica. Mona, Jamaica: Dept. of Extra-Mural Studies, University of the West Indies.
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.
Azevedo, N. R., Campos, I. F. P., Ferreira, H. D., Portes, T. A., Santos, S. C., Seraphin, J. C., … Ferri, P. H. (2001). Chemical variability in the essential oil of Hyptis suaveolens. Phytochemistry, 57(5), 733–736. https://doi.org/10.1016/S0031-9422(01)00128-5
Binns, S. E., Arnason, J. T., & Baum, B. R. (2002). Phytochemical variation within populations of Echinacea angustifolia (Asteraceae). Biochemical Systematics and Ecology, 30(9), 837–854. https://doi.org/10.1016/S0305-1978(02)00029-7
Blackwell, W. H. (1990). Poisonous and Medicinal Plants. Englewood Cliffs, NJ: Prentice Hall.
Boira, H., & Blanquer, A. (1998). Environmental factors affecting chemical variability of essential oils in Thymus piperella L. Biochemical Systematics and Ecology, 26(8), 811–822. https://doi.org/10.1016/S0305-1978(98)00047-7
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 (2nd ed.). Hoboken: Wiley-Blackwell.
Chang, C.-K., Chang, K.-S., Lin, Y.-C., Liu, S.-Y., & Chen, C.-Y. (2005). Hairy Root Cultures of Gynostemma pentaphyllum (Thunb.) Makino: A Promising Approach for the Production of Gypenosides as an Alternative of Ginseng Saponins. Biotechnology Letters, 27(16), 1165–1169. https://doi.org/10.1007/s10529-005-8653-7
Cipollini, D., & Gruner, B. (2007). Cyanide in the chemical arsenal of garlic mustard, Alliaria petiolata. Journal of Chemical Ecology, 33(1), 85–94. https://doi.org/10.1007/s10886-006-9205-x
Cui, J.-F., Eneroth, P., & Bruhn, J. G. (1999). Gynostemma pentaphyllum: identification of major sapogenins and differentiation from Panax species. European Journal of Pharmaceutical Sciences, 8(3), 187–191. https://doi.org/10.1016/S0928-0987(99)00013-5
Dahlgren, B. E. (1944). Edible and poisonous plants of the Caribbean region. The Supt. of Docs., U.S. G.P.O.
Dauncey, E. A. (2010). Poisonous Plants: A Guide for Parents & Childcare Providers. Kew: Royal Botanic Gardens, Kew.
Dhar, R. S., Verma, V., Suri, K. A., Sangwan, R. S., Satti, N. K., Kumar, A., … Qazi, G. N. (2006). Phytochemical and genetic analysis in selected chemotypes of Withania somnifera. Phytochemistry, 67(20), 2269–2276. https://doi.org/10.1016/j.phytochem.2006.07.014
Duke, J. A., & Foster, S. (2014). Peterson Field Guide to Medicinal Plants and Herbs of Eastern and Central North America (3rd Ed). Houghton Mifflin Harcourt.
Elpel, T. (2013). Botany in a Day: The Patterns Method of Plant Identification. (6th ed.). 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.
Hardin, J. W., & Arena, J. M. (1974). Human Poisoning from Native and Cultivated Plants (2nd ed). Durham, NC: Duke University Press.
He, K., Zhao, G.-X., Shi, G., Zeng, L., Chao, J.-F., & McLaughlin, J. L. (1997). Additional bioactive annonaceous acetogenins from Asimina triloba (Annonaceae). Bioorganic & Medicinal Chemistry, 5(3), 501–506. https://doi.org/10.1016/S0968-0896(96)00264-7
Jia, L., & Zhao, Y. (2009). Current Evaluation of the Millennium Phytomedicine- Ginseng (I): Etymology, Pharmacognosy, Phytochemistry, Market and Regulations. Current Medicinal Chemistry, 16(19), 2475–2484. https://doi.org/10.2174/092986709788682146
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.
Levine, R. A., Richards, K. M., Tran, K., Luo, R., Thomas, A. L., & Smith, R. E. (2015). Determination of Neurotoxic Acetogenins in Pawpaw (Asimina triloba) Fruit by LC-HRMS. Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/jf504500g
Lowe, H., Morrison, E., Magnus, K., & Campbell-Grizzle, E. (2004). Poisonous Plants of Jamaica: Their Toxins and Treatment. Kingston, Jamaica: Pelican Publishers Ltd.
McLaughlin, J. L. (2008). Paw paw and cancer: annonaceous acetogenins from discovery to commercial products. Journal of Natural Products, 71(7), 1311–1321. https://doi.org/10.1021/np800191t
Morton, J. F. (1971). Plants poisonous to people in Florida and other warm areas. Hurricane House.
Muenscher, W. C. (1940). Poisonous Plants of the United States. New York: MacMillan Publishing Co.
Nellis, D. W. (1997). Poisonous Plants and Animals of Florida and the Caribbean. Sarasota, FL: Pineapple Press.
Nelson, L. S., Shih, R. D., & Balick, M. J. (2007). Handbook of Poisonous and Injurious Plants (2nd ed.). New York: Springer.
Ogunwenmo, K. O., Idowu, O. A., Innocent, C., Esan, E. B., & Oyelana, O. A. (2007). Cultivars of Codiaeum variegatum (L.) Blume ( Euphorbiaceae ) show variability in phytochemical and cytological characteristics. African Journal of Biotechnology, 6(20). Retrieved from http://www.ajol.info/index.php/ajb/article/view/58071
Pammel, L. H. (1911). A Manual of Poisonous Plants. Chiefly of Eastern North America. Cedar Rapids, IA: The Torch Press.
Pomper, K. W., Lowe, J. D., Crabtree, S. B., & Keller, W. (2009). Identification of annonaceous acetogenins in the ripe fruit of the North American pawpaw ( Asimina triloba ). Journal of Agricultural and Food Chemistry, 57(18), 8339–8343. https://doi.org/10.1021/jf9018239
Potts, L. F., Luzzio, F. A., Smith, S. C., Hetman, M., Champy, P., & Litvan, I. (2012). Annonacin in Asimina triloba fruit: implication for neurotoxicity. Neurotoxicology, 33(1), 53–58. https://doi.org/10.1016/j.neuro.2011.10.009
Razmovski-Naumovski, V., Huang, T. H.-W., Tran, V. H., Li, G. Q., Duke, C. C., & Roufogalis, B. D. (2005). Chemistry and Pharmacology of Gynostemma pentaphyllum. Phytochemistry Reviews, 4(2–3), 197–219. https://doi.org/10.1007/s11101-005-3754-4
Rogers, R. D. (2014). Ancient medicinal remedies: horsetails, ferns, lichens and more.
Schlag, E. M., & McIntosh, M. S. (2006). Ginsenoside content and variation among and within American ginseng (Panax quinquefolius L.) populations. Phytochemistry, 67(14), 1510–1519. https://doi.org/10.1016/j.phytochem.2006.05.028
Scott, S., & Thomas, C. (2000). Poisonous Plants of Paradise: First Aid and Medical Treatment of Injuries from Hawaii’s Plants. Honolulu: University of Hawaii Press.
Searels, J. M., Keen, K. D., Horton, J. L., Clarke, H. D., & Ward, J. R. (2013). Comparing Ginsenoside Production in Leaves and Roots of Wild American Ginseng (Panax quinquefolius). American Journal of Plant Sciences, 04(06), 1252. https://doi.org/10.4236/ajps.2013.46154
Stewart, A. (2009). Wicked Plants: The Weed That Killed Lincoln’s Mother and Other Botanical Atrocities. Chapel Hill, NC: Algonquin Books.
Stuart, D. C. (2004). Dangerous garden: the quest for plants to change our lives. Cambridge, MA: Harvard University Press.
Turner, N. J., & Aderkas, P. von. (2009). The North American guide to common poisonous plants and mushrooms. Portland: Timber 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.
Ye, Q., Alfonso, D., Evert, D., & McLaughlin, J. L. (1996). Longifolicin, longicoricin, and gigantetroneninone, three novel bioactive mono-tetrahydrofuran annonaceous acetogenins from Asimina longifolia (annonaceae). Bioorganic & Medicinal Chemistry, 4(4), 537–545. https://doi.org/10.1016/0968-0896(96)00039-9
Zhao, G., Hui, Y., Rupprecht, J. K., McLaughlin, J. L., & Wood, K. V. (1992). Additional Bioactive Compounds and Trilobacin, a Novel Highly Cytotoxic Acetogenin, from the Bark of Asimina triloba. Journal of Natural Products, 55(3), 347–356. https://doi.org/10.1021/np50081a011
Zhao, G. X., Chao, J. F., Zeng, L., & McLaughlin, J. L. (1996). (2,4-cis)-asimicinone and (2,4-trans)-asimicinone: two novel bioactive ketolactone acetogenins from Asimina triloba (Annonaceae). Natural Toxins, 4(3), 128–134.
Zhao, G. X., Miesbauer, L. R., Smith, D. L., & McLaughlin, J. L. (1994). Asimin, asiminacin, and asiminecin: novel highly cytotoxic asimicin isomers from Asimina triloba. Journal of Medicinal Chemistry, 37(13), 1971–1976.