California Ivy, Hedera helix, also known as English Ivy, Common Ivy, Branching Ivy, Glacier Ivy, Needlepoint Ivy, Sweetheart Ivy, and simply Ivy, is a woody, evergreen, climbing or ground-creeping vine in the genus Hedera, within the family Araliaceae. Like other members within the genus, this plant has distinctive juvenile and adult life stages. In the juvenile stage, the plant will have characteristically lobed leaves and exhibit more herbaceous growth, often forming dense patches across the ground. The transition from juvenile to adult growth is generally triggered by the climbing of a host structure, such as a fence, wall, tree, trellis, or other vertical support. At that point, the plant develops woody vines, the leaves transition from lobed to unlobed, and the mature plant may eventually begin to produce umbels of small flowers on secondary branches.

Ivy is probably best known for its use in landscape decoration, and in 2010 it was estimated that approximately eight million potted ivy plants were sold in the United States alone. Ivy is not a newcomer to the field of decorative landscaping, having been used for that purpose for at least the last 300 years. During that time, a remarkable diversity of cultivars has been developed. Ivy, generically considered as Hedera spp., is native across portions of western, central, and southern Europe, Macaronesia, northwestern Africa, and central-southern Asia eastward to Japan and Taiwan.

Hedera helix is also one of the most recognizable ornamental vines in homes, gardens, landscapes, and older buildings. It may be grown as a houseplant, trained indoors in hanging baskets, used as groundcover, or allowed to climb walls, fences, and trees. This broad availability increases the likelihood of pet exposure, especially for cats that chew trailing houseplants, dogs that investigate landscaping, and horses or grazing animals that may encounter ivy growing along fence lines or woodland edges.

All species within the genus should be considered toxic or irritating to some degree, as they can cause a negative physical reaction when ingested or when they come into contact with unprotected skin. Pet Poison Helpline describes English Ivy as containing pentacyclic terpenoids, with expected signs after pet ingestion including drooling, vomiting, and diarrhea. NC State lists Hedera helix as poisonous, identifies triterpenoid saponins and polyacetylene compounds as the toxic principles, and notes that the foliage is more toxic than the berries.

The primary toxins include triterpenoid saponins, such as hederasaponin C, hederasaponin B, hederasaponosides B and C, alpha-hederin, and hederagenin. Another important irritant is the polyacetylene terpenoid falcarinol. Falcarinol, a polyyne, is capable of inducing a relatively severe allergic or irritant contact dermatitis reaction in the skin of some individuals and animals. The reflex-expectorant effect of ivy saponins has also contributed to the plant’s use by some individuals in the holistic community for the treatment of dry cough.

Like many species of potentially harmful plants, the actual toxicity or lethality of ivy, regardless of species, seems to have been greatly exaggerated in some sources. In Poisonous Plants in Britain and Their Effects on Animals and Man (1984), authors Cooper, M. R. and Johnson, A. W. note:

Cattle that ingested large quantities of English ivy vine became ill and excitable, started staggering, and bellowed loudly. The odor of crushed ivy leaves was on the breath and in the milk. Recovery was quick and complete in three days.

Additionally, this author was unable to find a single confirmed fatality, human, animal, or otherwise, caused by ingestion of any species in the genus Hedera. In fact, most reputable scientific and medical sources point out that the primary effect of ingestion seems to be limited to irritation of the digestive tract, generally manifesting as vomiting, diarrhea, coughing, drooling, abdominal pain, and oral irritation. Pet Poison Helpline likewise notes that severe signs, although reported experimentally, are not generally expected following ordinary pet exposure to English Ivy.

Hederin, one of the saponins isolated from the leaves of Hedera spp., is a strong and near-immediate irritant of the mucous membranes of the nose and throat. This tends to discourage all but the most stubborn animals from consuming anything more than a negligible amount of the plant. However, even with a small ingestion, there remains a risk of allergic or irritant contact dermatitis of the oral mucosa due to falcarinol and related compounds.

The associated discomfort may include redness, swelling, irritation, and blisters in the mouth or throat. In a sensitive animal, this discomfort could make eating or drinking difficult for a period of time, potentially necessitating veterinary care or fluid support to maintain adequate hydration. In the vast majority of household pet exposures, however, the expected course is short-lived gastrointestinal and oral irritation rather than life-threatening systemic poisoning.