Hedera, commonly called ivy (plural ivies), is a genus of 12–15 species of evergreen climbing or ground-creeping 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
On level ground ivies remain creeping, not exceeding 5–20 cm height, but on surfaces suitable for climbing, including
, natural rock
or man-made structures such as
quarry rock faces or built
masonry and
structures, they can climb to at least 30 m above the ground. Ivies have two
leaf types, with
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
are greenish-yellow with five small petals; they are produced in
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 , 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.[Ackerfield, J, & Wen, J. (2002). A morphometric analysis of Hedera L. (the ivy genus, Araliaceae) and its taxonomic implications. Adansonia sér. 3, 24: 197-212. Full text. ]
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.
Ivies are of major ecological importance for their nectar and fruit production, both produced at times of the year when few other nectar or fruit sources are available.[Hymettus — BWARS Information Sheet: Ivy Bee ( Colletes hederae) ] The fruit are eaten by a range of birds, including thrushes, , and .
A very wide range of invertebrates shelter and overwinter in the dense woody tangle of ivy.[ English Heritage - Ivy on Walls Seminar Report, 19 May 2010 www.geog.ox.ac.uk, accessed 11 November 2020] It serves to increase the surface area and complexity of woodland environments.
Taxonomy and evolution
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:
[McAllister, H. (1982). New work on ivies Int. Dendrol. Soc. Yearbook 1981: 106–109.][Germplasm Resources Information Network Species Records of Hedera ]
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Trichomes scale-like
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Hedera algeriensis Hibberd – Algerian ivy. Algeria, Tunisia (Mediterranean coast).
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Hedera canariensis Willd. – Canaries ivy. Canary Islands.
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Hedera colchica (K.Koch) K.Koch – Persian ivy. Alborz, Caucasus, Turkey.
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Hedera cypria McAllister – Cyprus ivy (syn. H. pastuchovii subsp. cypria (McAll.) Hand). Cyprus (Troodos Mts.)
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Hedera iberica (McAllister) Ackerfield & J.Wen – Iberian ivy. SW Iberian coasts.
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Hedera maderensis – Madeiran ivy. Madeira.
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Hedera maroccana McAllister – Moroccan ivy. Morocco.
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Hedera nepalensis K.Koch – Himalayan ivy (syn. H. sinensis (Tobl.) Hand.-Mazz.). Himalaya, SW China.
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Hedera pastuchovii G.Woronow – Pastuchov's ivy. Caucasus, Alborz.
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Hedera rhombea (Miq.) Siebold ex Bean – Japanese ivy. Japan, Korea, Taiwan.
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Trichomes stellate
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Hedera azorica Carrière – Azores ivy. Azores.
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Hedera crebrescens M. Bényei-Himmer et M. Höhn - Buda ivy. Central Europe
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Hedera helix L. – Common ivy (syn. H. caucasigena Pojark., H. taurica (Hibberd) Carrière). Europe, and widely introduced elsewhere.
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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).[R H Marshall, H A McAllister & J D Armitage (2017), A summary of hybrids detected in the genus Hedera (Araliaceae) with the provision of three new names, New Journal of Botany, 7:1, 2-8 [5]] Hybridisation may also have played a part in the evolution of some species in the genus.[Huxley, A., ed. (1992). New RHS Dictionary of Gardening 2: 60. Macmillan .][Metcalfe, D. J. (2005). Biological Flora of the British Isles no. 268 Hedera helix L. Journal of Ecology 93: 632–648.]
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
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
with variegated foliage and/or unusual leaf shapes have been selected for horticultural use.
The American Ivy Society is the International Cultivar Registration Authority for Hedera, and recognises over 400 registered cultivars.
Problems and dangers
On trees
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
Senescence trees supporting heavy ivy growth can be liable to
windthrow damage.
The UK's
Woodland Trust says "Ivy has long been accused of strangling trees, but it doesn’t harm the tree at all, and even supports at least 50 species of wildlife."
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.
Invasive exotic
Several ivy species have become a serious
invasive species (invasive exotic) in natural native plant
, 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
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
terpene 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.
Old regional common names in Britain, no longer used, include "Bindwood" and "Lovestone", for the way it clings and grows over stones and bricks. US
Pacific Coast regional common names for
H. canariensis include "California ivy" and "Algerian ivy". For
H. helix, regional common names include "common ivy" (Britain and Ireland) and "English ivy" (North America).
The name ivy has also been used as a common name for a number of other unrelated plants, including Boston ivy (Japanese creeper Parthenocissus tricuspidata, in the family Vitaceae), Cape-ivy (used interchangeably for Senecio angulatus and Delairea odorata, Asteraceae), poison-ivy ( Toxicodendron radicans, Anacardiaceae), Swedish ivy (whorled plectranthus Plectranthus verticillatus, Lamiaceae) and ground ivy ( Glechoma hederacea, also Lamiaceae), and Kenilworth ivy ( Cymbalaria muralis, Plantaginaceae).
Cultural symbolism
Like many other evergreen plants, which impressed European cultures by persisting through the winter, ivy has traditionally been imbued with a spiritual significance. It was brought into homes to drive out evil spirits.
In Ancient Rome it was believed that a wreath of ivy could prevent a person from becoming drunk, and such a wreath was worn by Bacchus, the god of intoxication.
Ivy bushes or ivy-wrapped poles have traditionally been used to advertise taverns in the United Kingdom, and many pubs are still called The Ivy.[ the-history-of-pub-names Ordnance Survey guides getoutside.ordnancesurvey.co.uk, accessed 11 November 2020]
Ivy's clinging nature makes it a symbol of love and friendship. There was once a tradition of priests giving ivy to newlyweds.
In medieval Christianity, it symbolized the soul's eternal life after death, because it clings to dead trees and remains green.[Dictionary of Symbolism: Cultural icons and the meaning behind them, by Hans Beidermann, translated by James Hulbert 1992 P.187]
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 Romanticism 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 university.
Ivy features extensively in the 2010 movie Arrietty and the poster for the film.
==Gallery==
See also
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Anjo Festival
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Bığbığ Ivy
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List of poisonous plants
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NASA Clean Air Study
External links
