| Hedera helix | |
|---|---|
| Adult leaves and fruit | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Asterids |
| Order: | Apiales |
| Family: | Araliaceae |
| Genus: | Hedera |
| Species: | H. helix |
| Binomial name | |
| Hedera helix L. |
|
Hedera helix (Common Ivy, English Ivy) is a species of ivy native to most of Europe and western Asia. It is labeled as an invasive species in a number of areas where it has been introduced.
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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 climbs by means of aerial rootlets which cling to the substrate.
The leaves are alternate, 50–100 mm long, with a 15–20 mm 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 autumn food source for bees and other insects.
The fruit are purple-black to orange-yellow berries 6–8 mm diameter, ripening in late winter, and are an important food for many birds, though somewhat poisonous to humans.
There are one to five seeds in each berry, which are dispersed by birds eating the berries.[1][2][3]
There are three subspecies:[1][4]
The closely related species Hedera canariensis and Hedera hibernica are also often treated as subspecies of H. helix,[3][5] though they differ in chromosome number so do not hybridise readily.[2] H. helix can be best distinguished by the shape and colour of its leaf trichomes, usually smaller and slightly more deeply lobed leaves and somewhat less vigorous growth, though identification is often not easy.[3][6]
It ranges from Ireland northeast to southern Scandinavia, south to Spain, and east to Ukraine and northern Turkey.
The northern and eastern limits are at about the -2°C winter isotherm, while to the west and southwest, it is replaced by other species of ivy.[1][2][3][4][5][7]
It is widely cultivated as an ornamental plant. Within its native range, the species is greatly valued for attracting wildlife. The flowers are visited by over 70 species of nectar-feeding insects, and the berries eaten by at least 16 species of birds. The foliage provides dense evergreen shelter, and is also browsed by deer.[1][8]
Over 30 cultivars have been selected for such traits as yellow, white, variegated (e.g. 'Glacier'), and/or deeply lobed leaves (e.g. 'Sagittifolia'), purple stems, and slow, dwarfed growth.[9]
The plant is considered invasive and destructive in parts of Australia and the United States. Its sale, transport or propagation is banned in several places.[10]
In the past, the leaves and berries were taken orally as an expectorant to treat cough and bronchitis.[11] In 1597, the British herbalist John Gerard recommended water infused with ivy leaves as a wash for sore or watering eyes.[12] The leaves can cause severe contact dermatitis in some people.[13][14] 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 contain the same allergen, falcarinol.
Like other exotic species, the invasion is due to human actions. H. helix is labeled as an invasive species in many parts of the United States, and its sale or import is banned in the state of Oregon. Ivies are plants adapted to the laurel forest, a type of cloud forest habitat. European Ivy for example, is believed was spread by birds in Europe, 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-colonize large areas when the weather was favorable again. With a great capacity of adaptation, find more favorable conditions for development and a more similar habitat to their historic european habitat. 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 opportunistic species across wide distribution with close vicariant relatives and few species, indicating the recent divergence of this species. The extant Ivy species of this group are relatively young. The expansion is favored by seeds spread by birds.[15]
It is considered a noxious weed across southern, particularly south-eastern, Australia and local councils provide free information and limited services for removal. In some councils it is illegal to sell the plant. It is a weed in the Australian state of Victoria.[16]
H. helix has been listed as an "environmental weed" by the Department of Conservation since 1990.[17]
In the United States, H. Helix is considered weedy or invasive in a number of regions and is on the official noxious weed lists of 46 states.[18] Like other invasive vines such as kudzu, H. helix can grow to choke out other plants and create "ivy deserts". State and county sponsored efforts are encouraging the destruction of ivy in forests of the Pacific Northwest and the Southern United States.[19][20] Its sale or import is banned in Oregon.[21] Ivy can easily escape from cultivated gardens and invade nearby parks, forests and other natural areas. Ivy can climb into the canopy of trees in such density that the trees fall over from the weight,[20] a problem which does not normally occur in its native range.[1] For this reason, it is especially important to remove ivy from trees, creating "survival rings". In its mature form, dense ivy can destroy habitat for native wildlife and creates large sections of solid ivy where no other plants can develop.[20]
Hedera is the generic term for Ivy. The species name helix derives from Ancient Greek "twist, turn" (see: Helix).
Synonyms include Hedera acuta, Hedera arborea ("tree ivy"),[22] Hedera baccifera, Hedera grandifolia,[23] English Ivy, Bindwood, and Lovestone.