Hedera helix

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) is a species of ivy native to most of Europe, from Ireland northeast to southern Scandinavia, south to Spain, and east to Ukraine and also northern Turkey in southwestern Asia. 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][6]}

The plant is considered invasive and destructive in parts of Australia and the United States. Its sale and cultivation is banned in several places.

Lobed juvenile leaves on climbing stems

Ivy growing on a granite crag, Czech Republic.

Stems showing the rootlets used to cling to walls and tree trunks.

Leaves of a variegated cultivar

Characteristics

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.^[5][2][6]

There are three subspecies:^[4][5]
•Hedera helix subsp. helix.
    Central, northern and western Europe. Plants without rhizomes. Purple-black ripe fruit.
•Hedera helix subsp. poetarum Nyman (syn. Hedera chrysocarpa Walsh).
    Southeast Europe and southwest Asia (Italy, Balkans, Turkey). Plants without rhizomes. Orange-yellow ripe fruit.
•Hedera helix subsp. rhizomatifera
    McAllister. Southeast Spain. Plants rhizomatiferous. Purple-black ripe fruit.

The closely related species Hedera canariensis and Hedera hibernica are also often treated as subspecies of H. helix,^[1][6] 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.^[6][7]

Other names and etymology

Synonyms include Hedera acuta, Hedera arborea Hort. ("tree ivy", propagations of adult crown material^[8]), Hedera baccifera, and Hedera grandifolia,^[9] and English Ivy. The species name helix derives from Ancient Greek "twist, turn".

Cultivation and uses

Hedera helix in Szczecin-Zdroje, Poland

Mixed green and yellow leaves of the cultivar 'Buttercup'

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.^[5][10]

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.^[11]

Ethnomedical uses

In the past, the leaves and berries were taken orally as an expectorant to treat cough and bronchitis.^[12] In 1597, the British herbalist John Gerard recommended water infused with ivy leaves as a wash for sore or watering eyes.^[13] Because of toxins also contained in the plant, it should only be used under the consultation of a qualified practitioner.^[14] The leaves can cause severe contact dermatitis in some people.^[15][16]

Ecological damage

Hedera helix is considered an invasive species in a number of areas to which it has been introduced, such as Australia^[17] and parts of the United States.^[18] Like other invasive vines, such as kudzu, it 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] 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. 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.^[5] 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]

References

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