Plants Toxic to Dogs and Cats—Redux

The U.S. is a nation of pet owners, and most of us feel a duty to protect those pets from various threats. Among the risks are toxins found in certain plants. Richard Lyons’ Nursery has addressed this subject before—just 18 months ago—but considers it important enough to merit repeating. Here is an expanded version of that column.

Many of us reside in southern Florida because of the wonderful winter climate that permits us not only to enjoy the great outdoors without bundling up, but also to cultivate thousands of tropical and temperate plants. However, as the old saying goes, there is no good unalloyed, and not every plant is benign. If you own a dog or cat, it behooves you to become familiar with the species that may harm your pet. Below you will find a list of a few of the plants known to affect pet health adversely. (Due to space limitations, this survey pertains only to dogs and cats. Besides, if your pet is a woolly mammoth, it’s probably better off indoors in an air-conditioned room.)

Ricinus communis (Castor Bean): While this species is the source of castor oil, it also possesses a darker side: Its seeds contain the highly toxic substance ricin, which received great attention after 9/11 as a means of conducting chemical/biological warfare. Ingestion of just a few seeds by a dog or cat can set up a fatal chain of neurological events.

Abrus precatorius (Rosary Pea): This species is not only an invasive exotic, but also the source of abrin, a highly toxic compound that occurs naturally in the plant’s seeds. Fortunately, an ingested seed is relatively harmless so long as its coating is intact. But if the surface has been scratched, crushed or otherwise damaged, the result can be deadly to both pets and their owners. In fact, abrin is more toxic than ricin.

Aglaonema, Alocasia, Colocasia, Dieffenbachia, Monstera, Philodendron, Spathiphyllum, Syngonium: Dumbcane, the common name for Dieffenbachia, provides a hint of the harm that these and other aroid species can cause. Ingestion of the calcium oxalate crystals found in the leaves of these plants can cause swelling inside the mouth of your pet (and humans may find themselves unable to speak). Dogs and cats may experience intense burning and swelling, along with drooling and vomiting.

Nerium oleander (Oleander): This flowering shrub, better-known simply as oleander, is an Old World native that has achieved widespread distribution throughout milder climates in the United States. Its dicey constituents are known as cardiac glycosides, and while they have beneficial medical applications, in the concentrations found in all parts of this plant they can be toxic to dogs and cats. Symptoms include diarrhea, sweating, poor coordination, compromised breathing, tremors, and abnormal cardiac functions. Even inhalation of the smoke of oleander trimmings being burned can be toxic.

Aloe vera (Aloe vera): This popular plant is well-known for providing relief for burns through application of its gel, but what’s good in it can also harm pets. Among the many chemical constituents of Aloe vera are saponins, which have long been used in soapmaking. However, when ingested by dogs or cats, saponins can cause anorexia, depression, diarrhea, and tremors.

Cycads: This ancient family has a dual personality. Cycads are both a food source and a toxin. An edible flour can be made from the pith inside the trunks of these plants, but only following considerable processing.  Underprocessed flour, along with the seeds and leaves of cycads, are toxic to humans and their pets, and significant ingestion can lead to severe neurological disorders. Where dogs and cats specifically are concerned, the leaflets are low-risk, since they are generally quite stiff and often edged with spines. The bigger threat is from seeds. The risk to your animals can be reduced by removing the cones of female cycads before they release their seeds.

Lycopersicon spp. (Tomato): Few people think of the tomato as potentially harmful to domestic pets, but its leaves contain the chemical solanine, which can cause the following symptoms in cats and dogs: loss of appetite, central nervous system depression, slow heart rate, drowsiness, diarrhea, confusion, severe gastrointestinal upset, weakness, dilated pupils, and behavioral change.

Brunfelsia nitida (Lady of the Night): A relative of tomato, this popular shrub can be quite toxic, more likely to dogs than cats, in the form of gastrointestinal or central nervous system disorders. Though all parts of the plant have toxic properties, the greatest risk is from ingestion of the berries. In most cases, prompt treatment will lead to full recovery.

Vinca spp. (Periwinkle): Here’s another example of a plant containing chemical constituents—in this case vinca alkaloids—which do both good and harm. While the compounds are used to treat certain cancers in humans, they can also cause severe problems when ingested by small pets, including low blood pressure, diarrhea, depression, tremors, vomiting, seizures, coma, and even death.

Asclepias spp. (Milkweed): What’s good for the monarch butterfly is not necessarily good for your dog or cat. Milkweed ingestion can cause a variety of symptoms: seizures, vomiting, respiratory distress, dilated pupils, weak pulse, cardiac arrhythmias, liver or kidney failure, coma, and death. Not all species of milkweed—there are 21 in Florida alone—are equally toxic, but it’s best to keep your pets away from them.

Asparagus densiflorus cv. Sprengeri (Asparagus Fern): This ubiquitous ground cover contains sapogenins, which can cause a lot of mischief in cats and dogs. If your pet is regularly exposed to the leaves of the plant, allergic dermatitis may set up. More significantly, ingestion of the berries of this plant can result in gastric problems such as abdominal pain, vomiting, and/or diarrhea.

Crassula arborescens (Silver Jade Plant): Unlike other species discussed in this article, the toxin at work here is unknown, but the dog or cat that takes a liking to the plump leaves of this succulent plant may soon find itself experiencing a bout of retching or nausea.

Allium cepa (Onion): We know that the onion is a heart-healthy vegetable for humans, but much less well-known is the fact that it may cause misery in pets, particularly cats. The culprit is N-propyl disulfide, which can cause a broad spectrum of symptoms, including gastrointestinal upset, breakdown of red blood cells, vomiting, weakness, panting, elevated heart rate, and blood in the urine.

Gloriosa superba (Gloriosa Lily): This herbaceous perennial produces beautiful, delicate flowers after lying dormant during the dry season. But it also produces colchicine-related alkaloids throughout the plant, and they can cause salivation, diarrhea, vomiting, kidney failure, shock, liver damage, and bone marrow suppression.

Kalanchoe spp. (Mother of Millions): These succulent plants tend to produce offspring, often in maddening numbers, interestingly at the margins of leaves. Most flower during the winter. The constituent which can affect your cat or dog is bufodienolides, which can cause diarrhea, vomiting and, occasionally, abnormal heart rhythm.

Citrus aurantifolia (Key Lime) and Citrus latifolia (Tahiti or Persian Lime): Ingestion of both these types of limes can cause distress in dogs and cats, including depression, vomiting and diarrhea. Furthermore, as in humans, exposure in sunlight to psoralens, oils found in the rinds of these fruits, can set up a very strong allergic response. (The risk of photosensitive reactions explains why limes grown commercially in Florida came to be packed within covered structures.)

Brugmansia spp. (Angel’s Trumpet): The seven species in this genus produce showy, pendant, trumpet-shaped flowers, but all plant parts contain toxic levels of tropane alkaloids which are capable of causing fatal reactions upon ingestion. At the very least, pets (and humans) who swallow the leaves, seeds or flowers of Brugmansias can experience blurred vision, dilated pupils, constipation, high blood pressure, and muscle weakness.

This list should in no way be considered all-inclusive; you are urged to research the topic on your own for additional information. You may want to start with the following informative sites:

Dogs: https://www.aspca.org/pet-care/animal-poison-control/dogs-plant-list
Cats: https://www.aspca.org/pet-care/animal-poison-control/cats-plant-list

The foregoing brief survey of toxic species found in southern Florida is not meant to alarm plant enthusiasts who also own cats and dogs. On the contrary, it should reassure you that despite being surrounded by germplasm that contains toxic substances, your pets seldom find themselves compromised. What we hope is that on the rare occasions when your dog or cat does ingest part of a toxic plant, you will recognize symptoms at a very early stage and make a call to your veterinarian for advice.

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