Getting Along with Wicked Plants

By Jenny Nelson, CCMGA Master Gardner

"Wicked plants" can be bad characters. From the carnivorous plant in Little Shop of Horrors to the screaming mandrakes, devil's snare and whomping willow in J.K. Rowling's Harry Potter series, our human anxieties rise at the mere sight of wicked plants that we fear could harm us. However, despite what we may have seen in Attack of the Killer Tomatoes, plants in the real world are neither wicked nor good. That they can kill or harm us is not a moral issue but one of science. Plants are complex organisms with adaptations that enable them to make toxic compounds called phytotoxins, which perform various biological functions.

Phytotoxins serve as a defensive mechanism for thousands of plants, certainly far too many to list here. Toxins can be present in leaves, stems, roots, flowers, berries, seeds or the entire plant. Although phytotoxins can sometimes be harmful, the more we know about them, the less we need to fear them.

Although poisonous plants surround us, human fatalities related to them are rare. Many plants we assume to be safe to eat also have some part of their anatomy that is poisonous, but we suffer no ill effects. Either we don't eat enough to reach the level of toxicity, or the poison is in a part of the plant that humans don't consume. Almonds and many stone fruits produce cyanide. Citrus fruits produce furocoumarins, stress toxins released when the plant is damaged. Plants from the nightshade family (tomatoes/potatoes/eggplants) produce the toxins solanine and chaconine in response to bruising, insect attacks or herbivore pressure.

Plants can use these phytotoxins to build symbiotic relationships with specialist insects. The connection between milkweed plants (Asclepias), seen to the left, and monarch butterflies is clear. In addition to the nectar that attracts pollinating insects, Milkweed plants produce a white latex sap that contains cardiac glycosides, compounds that can be highly poisonous to most animals but not to monarch butterflies. Monarchs can tolerate these toxins and use milkweed as host plants. After caterpillars consume milkweed and accumulate phytotoxins within their tissues, they become less appealing to predators. The plant responds to this robust caterpillar pruning by producing new growth and flowers, which increases seed production.

Humans, too, have discovered the hidden benefits of various toxic plants. Foxglove (Digitalis lanata) is a source of digoxin, a drug often used for patients with heart conditions. The toxins of the opium poppy (Papaver somniferum) have been used to make drugs like codeine and morphine. Modern scientists continue to study plant toxins, hoping to find more beneficial compounds.

We do not want to eradicate toxic plants from the wider native landscape since many animals depend on them for food and shelter. Poison ivy and native holly berries may be toxic for people, but the berries they produce are important food for birds and other animals. This is not to say you should have them by the front door!

Because plants can produce potentially harmful phytotoxins, we must be cautious. Just as we teach children to avoid strangers, it is important to teach them to avoid touching or eating strange plants. "Don't eat" and "Don't touch" are messages children need to hear. This is critical wherever berries and seeds are present, as these appeal to children. Closely supervise children around plants, as they can be more susceptible to the effects of toxins than adults.

Fortunately, plant-related fatalities are rare. According to America's Poison Centers, bad encounters with toxic plants rank 9th among their contact categories. Just because fatalities are rare doesn't mean we can relax our guard. The consequences of eating, touching or inhaling plant toxins can be serious. Toxic plant exposures can result in allergies, skin irritations, internal poisoning or physical injuries from thorns, spines or irritating hairs.

What Can We Do to Minimize Wicked Encounters?
• Identify toxic plants before bringing them home.
• Inventory plants and evaluate which may pose a risk to children or pets who may find them attractive, then make these plants hard to reach.
• Place toxic plants away from play areas and other high-traffic areas and avoid planting where children and pets cannot be supervised.
• Store bulbs and seeds out of the reach of children and pets.
• Never eat plants unless you are positive of their identification. Misidentification can have fatal results.
• When working where toxic plants like poison ivy may be found, wear protective gear.
• Don't use unknown twigs for various reasons (i.e., a stick to roast hot dogs).
• Teach young children not to forage for or eat any plant you have not permitted them to consume.
• Be aware that if young children see you eating an edible day lily petal, they may later copy that behavior with tragic results.
• Never experiment with unknown mushrooms. Mushrooms are plant-like fungi. More fatalities can be traced to eating mushrooms than from eating true plants.

 

 

 

 

Plants most frequently reported to poison control centers:
Pokeweed Phytolacca Americana (left image above)
Peace lilies Spathiphyllum
Holly Ilex
Philodendrons Monstera
Poison Ivy Toxicondendron

Additional common, but highly toxic plants*
Larkspur Delphinium consolida
Angel's Trumpet Datura
Castor Bean Plant Ricinus communis
Elephant Ears Colocasia, Alocasia
Foxglove Digitalis purpurea (right image above)
Juniper Juniperus
Oleander Nerium oleander (middle image above)
Azalea Rhododendron
Mistletoe Phoradendron tomentosum
Autumn Crocus Colchicum autumnale
*This is not a comprehensive list, and toxicity levels vary.

"An ounce of prevention is worth a pound of cure"
Researching the plants in your landscape is wise, and so is revising the landscape when the risks of owning a potentially wicked plant outweigh the rewards.

Questions? Ask the Experts
Contact your local state or regional poison control center for more specific information on this topic. For information on who to call or email in your area, visit the Poison Control and Prevention Center Directory. Of course, if you have someone who has collapsed or has trouble breathing, always call 911 before searching for a poison control center. For animal-related concerns, contact your veterinarian or ASPCA Animal Poison Control.
You can also find a list of toxic Texas plants through Texas A&M AgriLife Extension.