Ivy

"Hedera" redirects here. For the use of the term in typography, see Dingbat.

For other uses, see Ivy (disambiguation).

Hedera
Hedera rhombea, Aizu, Fukushima pref., Japan
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Apiales
Family:	Araliaceae
Subfamily:	Aralioideae
Genus:	Hedera L.
Species
See text

Ivy, plural ivies (Hedera) is a genus of 12–15 species of evergreen climbing or ground-creeping woody plants in the family Araliaceae, native to western, central and southern Europe, Macaronesia, northwestern Africa and across central-southern Asia east to Japan and Taiwan.

Description

Hedera helix adult leaves and unripe berries in Ayrshire, Scotland

On level ground they remain creeping, not exceeding 5–20 cm height, but on suitable surfaces for climbing, including trees, natural rock outcrops, or man-made structures such as quarry rock faces, 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 top 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

They are able to rise above the surface of trees and rocks, more than twenty or thirty meters above ground level. They are climbing plants with lauroide evergreen leaves that grow from the bottom of the ravines and river canyons lining the entire surface of the wall or cliff. Ivy climbs with adventitious roots and reaches up to 50 meter in length. Ivies are plants adapted to the laurel forest, a type of cloud forest habitat. European ivy for example, is believed,to have been spread by birds that helped to colonize large areas again where it had disappeared during the glaciations.

Laurus nobilis and Ilex aquifolium are widespread relics of the laurisilva forests that originally covered much of the Mediterranean Basin when the climate of the region was more humid. Ivy also is a relict plant and one of the survivors of the laurel forest flora in Europe tertiary era. Disappeared during the glaciations, ivy re-colonizes large areas when the weather was favorable again. With the drying of the Mediterranean during the Pliocene era, the laurel forests gradually retreated, and were replaced by the more drought-tolerant sclerophyll plant communities familiar today. Most of the last remaining laurisilva forests around the Mediterranean are believed to have disappeared approximately ten thousand years ago at the end of the Pleistocene era, when the Mediterranean Basin became drier and with a harsher climate. Today laurisilva forest persists in some continental and islanders enclaves and Macaronesia islands in the North Atlantic Ocean, which has moderated these climatic fluctuations.

The ecological requirements of the species, are those of the laurel forest and like most of their counterparts laurifolia in the world, it is a vigorous species with a great ability to populate the habitat that is conducive. Ivy responded to favourable climatic periods and expanded across the available habitat. Ivy occur as an opportunistic species across a wide distribution with close relatives and few species, indicating the recent divergence of this species. The extant ivy species of this group are relatively young. Seeds are spread by birds. Fruits are black and fleshy.

The Hedera genus has led to endemic species on islands, but not so widespread geographically as in the past. The species related from northeast Atlantic come from a species living in wet temperate areas and more distributed in the Tertiary. The main centers are found inhabiting wet lands in tropical or subtropical montane forests or coastal rainforest or coastal temperate forest in low-altitude. Hedera helix species have adapted to more extreme conditions but mostly depending on favorable soil edaphic conditions, as presence of aquifers, groundwater, rivers, periodic flows, etc.

The patterns of speciation in the Hedera genus, where ivy belongs, indicate that since the onset of aridification on the continent, it diversified in species with the majority of species the product of vicariance. The fragmentation of once more continuous area facilitated isolation of populations and this likely caused the increase in the rate of speciation as found in the Hedera helix and related species. In Europe the genus is represented by three native species, Hedera helix, Hedera iberica, and the named Hedera hibernica of Ireland island. In macaronesian islands Hedera canariensis arose from a common ancestor in the area of laurisilva in the Mediterranean area. The islander Hederas of Macaronesia in the eastern Atlantic, and Mediterranean sea, norther African Hederas and European Hederas are closely related species. Until recently it was thought there was a single species (Hedera helix), but recent studies have shown that there are several species that differ mainly by microscopic details of the hairiness of the buds. Hedera helix means Helix helix. Maroccana is the Latin patronymic of Morocco, where the Hedera maroccana species was described. The name of the other Hedera species come from Latin patronymic where the other species was described also.

The hederas islander species from Mediterranean sea and Atlantic Macaronesia can not endure a bad winter, from the continental climate. Those garden cultivated species outside its natural distribution could be killed by a continental winter.

Taxonomy

Hedera canariensis juvenile leaves, Gomera, Canary Islands.

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 pastuchowii 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 helix L. – Common ivy (syn. H. caucasigena Pojark., H. taurica (Hibberd) Carrière). Europe, widespread.
  • 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.

The only verified hybrid involving ivies is the intergeneric hybrid × Fatshedera lizei, a cross between Fatsia japonica and Hedera hibernica. This hybrid was produced once in a garden in France in 1910 and never successfully repeated, the hybrid being maintained in cultivation by vegetative propagation. Despite the close relationship between Hedera helix and H. hibernica (until relatively recently considered conspecific), no hybrids between them have yet been found. Hybridisation may however have played a part in the evolution of some species in the genus.

Uses and cultivation

File:Gwenyn ar Flodau Eiddew - Bees on ivy Flowers - geograph.org.uk - 547757.jpg

When the ivy flowers in September it is immediately crowded with bees and other nectar seekers.

A variegated Hedera helix cultivar

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. 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. 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.

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. Frank Lloyd Wright is attributed with saying "Doctors bury their mistakes, architects cover them with ivy".^{[citation needed]}

Problems and dangers

On trees

Much discussion has involved whether or not ivy climbing trees will harm them. In Europe the harm is insignificant although there can be competition for soil nutrients 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 caused by weakness from the duress.^{[citation needed]}

On walls

Concerns exist about damages 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 caliper, can be damaged or destroyed without ongoing training. 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 destabilising 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.^{[citation needed]}

Invasive exotic domination

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 ground-cover there, 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. Similar problems exist in Australia. For example, in both countries the North African drought-tolerant H. canariensis and H. algeriensis and European H. helix were originally cultivated in garden, park, and highway landscaping, but have become aggressively invasive in coastal forests and riparian ecosystems now necessitating costly eradication programs.

Toxicity

The berries are moderately toxic to humans, but are very bitter, so poisoning is rare. Ivy foliage contains triterpenoid saponins and falcarinol, a polyyne; falcarinol is capable of inducing an allergic reaction (contact dermatitis) in some people. People who have this allergy (strictly a Type IV hypersensitivity) are also likely to react to carrots and other members of the Apiaceae as they also contain falcarinol. It has also been shown to kill breast cancer cells.

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. U.S. Pacific Coast regional common names for H. canariensis include 'California ivy' and 'Algerian ivy', and for H. helix the generic 'English ivy'.

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 or German-ivy (Delairea odorata in the family Asteraceae), poison-ivy (Toxicodendron radicans in the family Anacardiaceae), and Swedish ivy (Whorled Plectranthus Plectranthus verticillatus, in the family Lamiaceae).

Gallery

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  Hedera helix on trees near Srbsko, Czech Republic

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  Hedera colchica leaves and flowers

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  Hedera hibernica with berries

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  Hedera helix leaves, Bremerhaven

• 

  Hedera helix flowers.

See also

• Delairea odorata - German ivy or Cape ivy.
• Parthenocissus tricuspidata - Boston ivy.
• Plectranthus verticillatus - Swedish ivy.
• Toxicodendron radicans - Poison ivy.
• List of air-filtering plants