Hedera, commonly called ivy (plural ivies), is a genus of 12–15 species of evergreen climbing or ground-creeping woody plants in the family Araliaceae, native to Western Europe, Central Europe, Southern Europe, Macaronesia, northwestern Africa and across central-southern Asia east to Japan and Taiwan. Several species are cultivated as climbing ornamentals, and the name ivy especially denotes common ivy (Hedera helix), known in North America as "English ivy", which is frequently planted to clothe brick walls.

Description

right|thumb|[[Hedera helix adult leaves and unripe berries in Ayrshire, Scotland]]

On level ground ivies remain creeping, not exceeding 5–20 cm height, but on surfaces suitable for climbing, including trees, natural rock outcrops or man-made structures such as quarry rock faces or built masonry and wooden structures, they can climb to at least 30 m above the ground. 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 tops of rock faces, from 2 m or more above ground. The juvenile and adult shoots also differ, the former being slender, flexible and scrambling or climbing with small aerial roots to affix the shoot to the substrate (rock or tree bark), the latter thicker, self-supporting and without roots. The flowers are greenish-yellow with five small petals; they are produced in umbels in autumn to early winter and are very rich in nectar. The fruit is a greenish-black, dark purple or (rarely) yellow berry 5–10 mm diameter with one to five seeds, ripening in late winter to mid-spring. The seeds are dispersed by birds which eat the berries.

The species differ in detail of the leaf shape and size (particularly of the juvenile leaves) and in the structure of the leaf trichomes, and also in the size and, to a lesser extent, the colour of the flowers and fruit. The chromosome number also differs between species. The basic diploid number is 48, while some are tetraploid with 96, and others hexaploid with 144 and octaploid with 192 chromosomes.

Ecology

Ivies are natives of Eurasia and North Africa, but have been introduced to North America and Australia. They invade disturbed forest areas in North America. Ivy seeds are spread by birds. The ivy bee Colletes hederae is completely dependent on ivy flowers, timing its entire life cycle around ivy flowering. The fruit are eaten by a range of birds, including thrushes, blackcaps, and woodpigeons. It serves to increase the surface area and complexity of woodland environments.

Taxonomy and evolution

thumb|right|[[Hedera canariensis juvenile leaves, Gomera, Canary Islands.]]

thumb|[[Hedera algeriensis]]

The following species are widely accepted; they are divided into two main groups, depending on whether they have scale-like or stellate trichomes on the undersides of the leaves:

  • Trichomes scale-like
  • Hedera algeriensis Hibberd – Algerian ivy. Algeria, Tunisia (Mediterranean coast).
  • Hedera canariensis Willd. – Canaries ivy. Canary Islands.
  • Hedera colchica (K.Koch) K.Koch – Persian ivy. Alborz, Caucasus, Turkey.
  • Hedera cypria McAllister – Cyprus ivy (syn. H. pastuchovii subsp. cypria (McAll.) Hand). Cyprus (Troodos Mts.)
  • Hedera iberica (McAllister) Ackerfield & J.Wen – Iberian ivy. SW Iberian coasts.
  • Hedera maderensis – Madeiran ivy. Madeira.
  • Hedera maroccana McAllister – Moroccan ivy. Morocco.
  • Hedera nepalensis K.Koch – Himalayan ivy (syn. H. sinensis (Tobl.) Hand.-Mazz.). Himalaya, SW China.
  • Hedera pastuchovii G.Woronow – Pastuchov's ivy. Caucasus, Alborz.
  • Hedera rhombea (Miq.) Siebold ex Bean – Japanese ivy. Japan, Korea, Taiwan.
  • Trichomes stellate
  • Hedera azorica Carrière – Azores ivy. Azores.
  • Hedera crebrescens M. Bényei-Himmer et M. Höhn - Buda ivy. Central Europe
  • Hedera helix L. – Common ivy (syn. H. caucasigena Pojark., H. taurica (Hibberd) Carrière). Europe, and widely introduced elsewhere.
  • Hedera hibernica (G.Kirchn.) Bean – Atlantic ivy (syn. H. helix subsp. hibernica (G.Kirchn.) D.C.McClint.). Atlantic western Europe.

The species of ivy are largely allopatric and closely related, and many 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.

Hybrids have been recorded between several Hedera species, including Atlantic ivy (H hibernica) with common ivy (H helix). Hybridisation may also have played a part in the evolution of some species in the genus.

Evolution

The genus is thought to have originated in East Asia, with the earliest fossil of the genus being known from Korea, dating to the Oligocene epoch. The genus later expanded westwards, reaching Europe during the early-middle Miocene epoch.

Uses and cultivation

thumb|right|180px|When the ivy blooms in September it attracts [[hoverfly|hoverflies and other nectar feeders.]]

right|thumb|180px|A variegated Hedera helix cultivar

Ivies are very popular in cultivation within their native range and compatible climates elsewhere, for their evergreen foliage, attracting wildlife, and for adaptable design uses in narrow planting spaces and on tall or wide walls for aesthetic addition, or to hide unsightly walls, fences and tree stumps. Numerous cultivars with variegated foliage and/or unusual leaf shapes have been selected for horticultural use.

Problems and dangers

On trees

thumb|Ivy climbing on a pine tree ([[Pinus sylvestris) in Headley, UK. ]]

Much discussion has involved whether or not ivy harms the trees it climbs. In Europe, the harm is generally minor although there can be competition for soil nutrients, light, and water, and senescent trees supporting heavy ivy growth can be liable to windthrow damage. Harm and problems are more significant in North America, where ivy is without the natural pests and diseases that control its vigour in its native continents; the photosynthesis or structural strength of a tree can be overwhelmed by aggressive ivy growth leading to death directly or by opportunistic disease and insect attacks.

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On walls

Concerns exist about damage by aerial roots and trunk growth to dry stacked stone, brick or stone and mortar, and stucco-plastered walls. Dry stacked stonework, over enough time for ivy trunks to gain significant girth, can be damaged or destroyed. For brick or stone and mortar construction it is of general opinion that a soundly mortared installation is impenetrable to the climbing aerial roots and thus not damaged, and even protected from weathering by the ivy deflecting rain impact off the mortar. However, walls with preexisting weakened or loose mortar may be badly damaged, as the ivy's roots penetrate the mortar and break up the wall. Subsequent ivy removal can be difficult, and often causes further damage. Modern mortars containing Portland cement and little lime are stronger than older mortar mixes composed of just sand and lime. Most mortar mixes began containing Portland cement in the 1930s. Older mortar mixes are still used for laying softer types of bricks. Stucco and plaster walls can be aesthetically ruined after ivy pruning or removal, requiring a new topcoat or repainting, and sometimes needing restoration for structural and waterproofing problems. When ivy climbs on wooden structures and fences, there can be direct and secondary problems. The direct issues are runners and trunks growing between boards and expanding construction joints, thus destabilizing or destroying the structure. The secondary issues involve the entry of aerial roots into the wood grain causing the wood to split and allowing moisture and fungus to penetrate and accelerate wet rot and eventual collapse. -->

Invasive exotic

Several ivy species have become a serious invasive species (invasive exotic) in natural native plant habitats, especially riparian and woodland types, and also a horticultural weed in gardens of the western and southern regions of North America with milder winters. Ivies create a dense, vigorously smothering, shade-tolerant evergreen groundcover that can spread through assertive underground rhizomes and above-ground runners quickly over large natural plant community areas and outcompete the native vegetation. The use of ivies as ornamental plants in horticulture in California and other states is now discouraged or banned in certain jurisdictions. Drought-tolerant H. canariensis and H. algeriensis and European H. helix were originally cultivated in garden, park, and highway landscaping, but they have become aggressively invasive in coastal forests and riparian ecosystems, now necessitating costly eradication programs. Similar problems exist in Australia. Only one species of ivy, H. helix , bears the status of 'declared weed' in Australia; in the Australian Capital Territory, and Western Australia only.

Toxicity

The berries are moderately toxic to humans. Ivy foliage contains triterpenoid saponins and falcarinol.

Falcarinol is capable of inducing contact dermatitis. It has also been shown to kill breast cancer cells.

Stinging insects

The flowers of ivy are pollinated by Hymenoptera and are particularly attractive to the common wasp.

Etymology and other names

The name ivy derives from Old English ifig, cognate with German Efeu, of unknown original meaning. The scientific name Hedera is the classical Latin name for the plant.

Ivy's clinging nature makes it a symbol of love and friendship. There was once a tradition of priests giving ivy to newlyweds.

The traditional British Christmas carol, "The Holly and the Ivy", uses ivy as a symbol for the Virgin Mary.

Ivy-covered ruins were a staple of the Romantic movement in landscape painting, for example Visitor to a Moonlit Churchyard by Philip James de Loutherbourg (1790), Tintern Abbey, West Front by Joseph Mallord William Turner (1794) and Netley Abbey by Francis Towne (1809). In this context, ivy may represent the ephemerality of human endeavours and the sublime power of nature.

The image of ivy-covered historic buildings gave the name Ivy League to a group of old and prestigious American universities.

Ivy features extensively in the 2010 movie Arrietty and the poster for the film.

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File:Beroun, Hostim, popínavé rostliny v údolí říčky Loděnice-Kačák.JPG|Hedera helix on trees near Srbsko, Czech Republic

File:Hedera colchica0.jpg|Hedera colchica leaves and flowers

File:Hedera hibernica with berries.JPG|Hedera hibernica with berries

File:Ivy 77uf be.JPG|Hedera helix leaves, Bremerhaven

File:Hedera helix 003.JPG|Hedera helix flowers

</gallery>

See also

  • Anjo Festival
  • Bığbığ Ivy
  • List of poisonous plants
  • NASA Clean Air Study

References

  • Kew plant profiles: Hedera helix (common ivy)