Hedera helix (L.)

English Ivy

Araliaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (Flowering plants). Class - Magnoliopsida (Dicotyledons). Subclass - Rosidae. Order - apiales. Family - Araliaceae (Ginseng family). Genus - Hedera L.. Species - Hedera helix L. (English ivy).

Identification: English ivy is a woody, evergreen, trailing or climbing liana or shrub. In Europe, English ivy occasionally grows as a tree. English ivy has 2 distinct growth phases, the vegetative phase (juvenile) and the sexual reproductive phase (adult). Individual English ivy plants may have both juvenile and adult stems. The juvenile phase typically forms the ground cover. Juvenile English ivy begins to climb when vertical structure is available (e.g., trees, shrubs, buildings, utility poles), and vertical stems transition to the adult phase.

As a ground cover, English ivy grows from 10-20 cm tall. Once stems begin climbing, they typically reach 30 m in height but occasionally may climb higher, reaching the tops of 90 m conifers. English ivy climbs with the aid of root-like structures that exude an adhesive substance. Branches are typically slender on low-growing plants, but climbing and older trailing branches may be 10-30 cm in diameter, with furrowed bark. Leaves are typically 10 cm long, 6.4-13 cm wide and are 3 to 5 lobed in the juvenile phase and broadly lanceolate and unlobed in the adult phase. Flowers are clustered in umbels on adult stems.

English ivy's photosynthetic capacity adjusts for variable light levels; to what degree may be determined by the life phase (juvenile or adult) of the plant. In general, adult leaves have a greater photosynthetic capacity than juvenile leaves, even on the same plant... In some locations, English ivy may reach its greatest abundance in shade... English ivy's tolerance to a wide range of light levels suggests it may establish and/or persist throughout most successional stages.

Threats

Reports on English ivy's impacts within its North American range are variable. English ivy threatens native plant communities and wildlands in Oregon, California, Washington D.C., Kentucky, Georgia, and Alabama. It is a potential threat in the upper Great Lakes areas, Missouri, and Tennessee. English ivy is a particularly serious threat to native plant communities in the coastal Pacific Northwest states and was placed on Oregon's list of quarantine species in 2010.

One report from the Pacific Northwest suggested that English ivy may decrease water quality and increase erosion. Researchers have identified English ivy as a host for bacterial leaf scorch (Xylella fastidiosa), a plant pathogen that harms native trees including elms, oaks, and maples. There is some concern that leaf litter from English ivy increases soil nitrogen, which may negatively impact native plant species that grow best in low nutrient conditions. It has been suggested that the best way to prevent English ivy invasion is to avoid growing it near forests; however, since its seeds are dispersed by birds, this may not prevent its invasion entirely.

Reproduction

Vegetative Regeneration - English ivy sprouts from stem fragments and cut stumps. Stems and stem fragments root easily when they are in contact with the soil. and plants spread from adventitious roots that develop along the stem. Fragmented roots left in the soil may sprout a new stem. Both trailing and climbing vines spread by rooting at the nodes.

Flowering and Fruiting - Sexual reproduction typically occurs in climbing adult plants that reach sufficient light, but trailing plants may occasionally produce fruit, especially if they are growing in full sunlight. English ivy flowers are bisexual and cross-pollinated by a wide variety of insects. In the Netherlands, pollen counts collected from various sampling sites (e.g., water trough, roof tiles, moss on a thatched roof) in October determined that one large, profusely flowering English ivy produced several billion pollen grains annually. English ivy seed is dispersed by birds. After digesting the fruit, birds may regurgitate English ivy seed one at a time.

Seedling Establishment - English ivy seedlings may also establish under forest or shrub canopy; however, growth rate may be less than for unshaded seedlings. English ivy seedlings were moderately tolerant of shade under drought conditions. Seedlings are shallowly rooted and grow a single, slender, vertical primary root that bears many short, fine branches, some of which develop into horizontal secondary and lateral stem. English ivy begins to climb when it reaches a vertical structure, taking approximately 30 to 40 years to reach tree canopies, but growth may be faster on flooded sites.

Species Distribution

Citation

USFS Plant Database

USDA Plant Databse