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Hedera

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"Hedera" redirects here. For the typographic ornamentation, see fleuron (typography).
For other uses, see Hedera (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

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 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.[1]

Ecology

Ivies are natives of Eurasia and north Africa but have been introduced to North America where they can be invasive.[2][dead link] The speciation of ivies probably began around the Mediterranean Basin.[2] 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.[3] The Ivy Bee Colletes hederae is completely dependent on ivy flowers, timing its entire life cycle around ivy flowering.[4] The fruit are eaten by a range of birds, including thrushes, blackcaps, and woodpigeons.[3] 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.

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:[1][5][6]

  • Trichomes scale-like
  • 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.[7][8] Despite the close relationship between Hedera helix and H. hibernica (until relatively recently considered conspecific), no hybrids between them have yet been found.[9] Hybridisation may however have played a part in the evolution of some species in the genus.[1]

Uses and cultivation

When the ivy flowers in September it attracts with hoverflies and other nectar feeders.
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.[7] 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.[3] 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.[10] 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.[11]

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.[12]

Etymology and other names

The name ivy derives from Old English ifig, cognate with German Efeu, of unknown original meaning.[13] The scientific name Hedera is the classical Latin name for the plant.[7] 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).

  • Hedera helix on trees near Srbsko, Czech Republic
    Hedera helix on trees near Srbsko, Czech Republic
  • Hedera colchica leaves and flowers
    Hedera colchica leaves and flowers
  • Hedera hibernica with berries
    Hedera hibernica with berries
  • Hedera helix leaves, Bremerhaven
    Hedera helix leaves, Bremerhaven
  • Hedera helix flowers.
    Hedera helix flowers.

See also

References

  1. ^ a b c 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.
  2. ^ a b Bioone Retrieved May 21st 2012
  3. ^ a b c Mitchell, A. F. (1975). Three Forest Climbers. Forestry Commission Forest Record 102.
  4. ^ Hymettus — BWARS Information Sheet: Ivy Bee (Colletes hederae)
  5. ^ McAllister, H. (1982). New work on ivies Int. Dendrol. Soc. Yearbook 1981: 106–109.
  6. ^ Germplasm Resources Information Network Species Records of Hedera
  7. ^ a b c Huxley, A., ed. (1992). New RHS Dictionary of Gardening 2: 60. Macmillan ISBN 0-333-47494-5.
  8. ^ Metcalfe, D. J. (2005). Biological Flora of the British Isles no. 268 Hedera helix L. Journal of Ecology 93: 632–648.
  9. ^ McAllister, H.A., & Rutherford, A. (1990). Hedera helix L. and H. hibernica (Kirchner) Bean (Araliaceae) in the British Isles. Watsonia 18: 7-15. Full text.
  10. ^ "Criteria for Categorizing Invasive Non-native Plants that Threaten Wildlands" (PDF). Cal-IPC. 2003-02-28. Retrieved 2010-04-01.. {{cite web}}: Check date values in: |accessdate= and |date= (help)
  11. ^ "California Invasive Plant Council Interactive Database". Cal-IPC. Retrieved 2010-02-02.. {{cite web}}: Check date values in: |accessdate= (help)
  12. ^ M. Kobæk-Larsen, L. P. Christensen, W. Vach, J. Ritskes-Hoitinga and K. Brandt (2005). "Inhibitory Effects of Feeding with Carrots or (-)-Falcarinol on Development of Azoxymethane-Induced Preneoplastic Lesions in the Rat Colon". Journal of Acricultural and Food Chemistry. 53 (5): 1823–1827. doi:10.1021/jf048519s. PMID 15740080.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ The Oxford Dictionary of English Etymology
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