English Ivy is the common name for the specific plant species, Hedera helix, which belongs to the larger genus Hedera. While all English Ivy is Hedera, the genus includes several other distinct species often called “ivy.” These species share similar characteristics but are scientifically different plants.
The Taxonomy of Ivy
The genus Hedera contains approximately 12 to 15 species of evergreen, woody, climbing, or ground-creeping plants. These species belong to the Araliaceae family (ginseng family) and are native to Western and Central Europe, parts of Asia, and North Africa.
Hedera helix is the most widely known species, earning the common name English Ivy. Other recognized species include Hedera hibernica (Irish Ivy), Hedera colchica (Persian Ivy), and Hedera canariensis (Canary Island Ivy). Although closely related, these species are distinct entities with their own geographical ranges and slight morphological differences. For example, H. hibernica is now recognized as a separate species from H. helix due to differences in chromosome count and leaf characteristics.
Distinguishing English Ivy from Related Species
Identifying Hedera helix involves observing its two distinct growth phases. The juvenile phase is the most common form, seen as groundcover or climbing walls. Its leaves are typically three- to five-lobed, glossy, and dark green. The plant climbs using small, aerial rootlets that cling to surfaces like masonry or tree bark.
Once the vine reaches sufficient height and sunlight, it matures into its adult phase, usually after about ten years. The leaves on these reproductive stems lose their lobes, becoming more ovate or heart-shaped. The plant develops a bushier, self-supporting growth habit, and these mature stems are the only ones that produce greenish-yellow flowers and subsequent berries. Distinguishing English Ivy from close relatives, such as Irish Ivy, sometimes requires examining the microscopic hairs (trichomes) on the leaves.
Safety and Environmental Concerns
Many Hedera species, especially Hedera helix, pose risks related to toxicity and environmental impact. The plant contains triterpenoid saponins, such as hederagenin, which cause toxicity. Ingestion of the leaves or the black, berry-like fruits can cause adverse reactions in humans and pets, including vomiting, abdominal pain, diarrhea, and excessive drooling.
Contact with the sap can also cause allergic contact dermatitis in sensitive individuals. Ecologically, English Ivy is classified as an invasive species outside of its native range. Its aggressive growth forms dense mats of foliage that smother native groundcover plants, severely reducing biodiversity. When climbing trees, the heavy vines increase storm damage susceptibility and block sunlight, inhibiting the tree’s ability to photosynthesize and leading to its decline.