Hedera - Ivy

Hedera (English name ivy) 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.

They 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.


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 particularly valuable for covering unsightly walls.

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.

Much has been argued as to whether ivy climbing trees will harm the tree or not; 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.


Species
Hedera helix, also called Ivy, Common Ivy, or English Ivy is a species of ivy native to most of Europe,along the west coast of South America, southwest Asia and Australia. It is an evergreen climbing plant, growing to 20-30 m high where suitable surfaces (trees, cliffs, walls) are available, and also growing as ground cover where there are no vertical surfaces. It holds on to tree bark and rock by means of short adhesive rootlets. The helix part of the name refers to where there are spirals in the leaves.
The leaves are alternate, 50-100 long, with a 15-20 cm long petiole; they are of two types, with palmately five-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 flowers are produced from late summer until 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.
It is widely cultivated as an ornamental plant, with numerous cultivars selected for such traits as yellow, pure white, variegated and/or a deeply lobated leaves, purple stems, and slow, dwarfed growth.

Hedera hibernica is a species of Ivy (genus Hedera) which is native to the Atlantic coast of Europe. Its common names are the Atlantic Ivy or Irish Ivy.

Hedera algeriensis – Algerian Ivy

Hedera canariensis – Canaries Ivy

Hedera maderensis – Madeiran Ivy

Hedera maroccana

Hedera rhombea – Japanese Ivy

Hedera sinensis

Hedera taurica

Hedera caucasigena

Hedera colchica – Caucasian Ivy

Hedera nepalensis – Himalayan Ivy

Hedera cypria

Hedera azorica – Azores Ivy

Hedera pastuchowii – Pastuchov's Ivy

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