The biology of Canadian weeds: 157. Hedera helix L. and Hedera hibernica (G. Kirchn.) bean.
Two related species of Hedera spp. exist throughout Canada: English Ivy (Hedera helix L.) and Irish Ivy [Hedera hibernica (G. Kirchn.) Bean]. These species are difficult to distinguish taxonomically and clear distinctions are not always made in the literature, so we largely discuss them as a single taxon in this account. Ivy is an evergreen perennial with two distinct forms: woody vine (juvenile form) or shrub (adult form). In Canada, Hedera spp. are found naturalized along the southern coast of British Columbia (Vancouver, Vancouver Island, and the Gulf Islands) and in southwestern Ontario. During the past century, ivies have greatly expanded their ranges along the Pacific and Atlantic coasts of North America and in New Zealand, Australia, South Africa, Brazil, and Hawaii. Ivy is physiologically plastic, invading both semi-open and deeply shaded forests. It forms a dense ground cover that can inhibit native vegetation. It grows up on tree trunks and competes for soil nutrients, frequently leading to tree damage or even tree fall. Invasive characteristics include its evergreen habit, persistence, and vegetative reproductive capabilities. Humans have accelerated the spread of ivy by planting it along highway embankments and medians to control soil erosion and through widespread sale as an ornamental plant. There is debate among horticulturalists and ecologists over the destructive and advantageous effects of ivy growth and sale within North America. Various methods of control (chemical, manual, biological, and integrated) may be used to manage this species, but more research is needed to design better control techniques.