Hedera

Hedera
	Hedera colchica
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Apiales
Family:	Araliaceae
Subfamily:	Aralioideae
Genus:	Hedera; L.
Species
	Hedera algeriensis – Algerian Ivy; Hedera azorica – Azores Ivy; Hedera canariensis – Canaries Ivy; Hedera caucasigena; Hedera colchica – Caucasian Ivy; Hedera cypria; Hedera helix – Common Ivy or English Ivy; Hedera hibernica – Irish Ivy; Hedera maderensis – Madeiran Ivy; Hedera maroccana; Hedera nepalensis – Himalayan Ivy; Hedera pastuchowii – Pastuchov's Ivy; Hedera rhombea – Japanese Ivy; Hedera sinensis; Hedera taurica;

Hedera (Template:Pron-en;^[1] English name ivy, plural ivies) is a genus of 15 species of climbing or ground-creeping evergreen woody plants in the family Araliaceae, native to the Atlantic Islands, western, central and southern Europe, northwestern Africa and across central-southern Asia east to Japan. On suitable surfaces (trees and rock faces), they are able to climb to at least 25–30 metres above the basal ground level.

Regional English common names for ivy include Bindwood and Lovestone (for the way it clings and grows over stones and brickwork).

True ivy must not be confused with Boston Ivy and to a lesser extent Virginia creeper, both of which are climbers that can grow up buildings, but are deciduous rather than evergreen, and are quite unrelated to true ivy, both being of the grape family. It should also not be confused with cape ivy, which is in the sunflower family.

Description

Ivies have two leaf types, with palmately lobed juvenile leaves on creeping and climbing stems, and unlobed cordate adult leaves on fertile flowering stems exposed to full sun, usually high in the crowns of trees or the top of rock faces. The juvenile and adult shoots also differ, the former being slender, flexible and scrambling or climbing with small roots to affix the shoot to the substrate (rock or tree bark), the latter thicker, self-supporting, and without roots.

The flowers are produced in late autumn, individually small, in 3–5 cm diameter umbels, greenish-yellow, and very rich in nectar, an important late food source for bees and other insects; the fruit are small black berries ripening in late winter, and are an important food for many birds, though poisonous to humans. The seeds are dispersed by birds eating the fruit.

The leaves are eaten by the larvae of some species of Lepidoptera such as Angle Shades, Lesser Broad-bordered Yellow Underwing, Scalloped Hazel, Small Angle Shades, Small Dusty Wave (which feeds exclusively on ivy), Swallow-tailed Moth and Willow Beauty.

Ivy and vines are living, growing, and moving organisms that attach to more static objects. On a building, this can result in displacement of building parts. Some vines, like wisteria, climb by twinning around objects. Not only does this type of vine get a firm grip but the diameter of the vine increases with maturity, constricting around the object.^[2]

Taxonomic note

The species of ivy are largely allopatric and closely related, and all have on occasion been treated as varieties or subspecies of H. helix, the first species described. Several additional species have been described in the southern parts of the former Soviet Union, but are not regarded as distinct by most botanists.

Uses and cultivation

Ivies are very popular in cultivation within their native range, both for attracting wildlife, and for their evergreen foliage; many cultivars with variegated foliage and/or unusual leaf shape have been selected. They are often used to cover unsightly walls while furnishing their own aesthetic appeal.

Ivies have however proved to be a serious invasive weed in the parts of North America where winters are not severe, and their cultivation there is now discouraged in many areas. Similar problems exist in Australia where the plant was originally cultivated in gardens. For example, in the coastal basins of California drought-tolerant Algerian ivy (H. algeriensis or H. canariensis) has been planted as a ground cover around buildings and highways, but it has become an invasive weed in coastal forests, and riparian areas.^[3]

Much has been argued as to whether or not an ivy climbing a tree will cause harm to it; the consensus in Europe is that they do not harm trees significantly, though they may compete for ground nutrients and water to a small extent, and trees with a heavy growth of ivy can be more liable to windthrow. Problems are greater in North America, where trees may be overwhelmed by the ivy to the extent they are killed; this could be because ivy in North America, being introduced, is without the natural pests and diseases that control its vigour in its native areas. A more serious problem is that ivy creates a vigorous, dense, shade-tolerant evergreen groundcover (precisely the characteristics for which it is often cultivated) that can spread over large areas and outcompete native vegetation.

Similar concerns are expressed about damage to walls. It is generally considered that a soundly mortared wall is impenetrable to the climbing roots of ivy and will not be damaged, and is also protected from further weathering, by the ivy keeping rain off the mortar. Walls with already weak or loose mortar may however be badly damaged, as the ivy is able to root into the weak mortar and further break up the wall. Subsequent removal of the ivy can be difficult, and is likely to cause more damage than the ivy itself. Modern mortars that contain portland cement and little lime are stronger than older mortar mixes that were largely composed of just sand and lime. Most mortar mixes changed to contain Portland cement in the 1930s. Soft mortar is still used when laying softer brick. If ivy is allowed to climb wooden structures, then the aerial roots are likely to enter into the wood grain causing the wood to split, allowing moisture and fungus to penetrate the wood and accelerating wet rot.

Toxicity

Although far less toxic than poison ivy, which is unrelated to this genus, ivy contains triterpenoid saponins and falcarinol, a polyyne. Falcarinol is capable of inducing an allergic reaction (contact dermatitis).^[4] It has also been shown to kill breast cancer cells.