Hedera helix, the common ivy, English ivy, European ivy, or just ivy, is a species of flowering plant in the family Araliaceae, native to most of Europe and western Asia. A rampant, clinging evergreen vine, it is a familiar sight in gardens, waste spaces, on house walls, tree trunks and in wild areas across its native habitat.
- 1 Etymology
- 2 Synonyms
- 3 Description
- 4 Range
- 5 Cultivation and uses
- 6 Invasive species
- 7 Control and eradication
- 8 Damage to trees
- 9 Use as building facade green
- 10 Mechanism of attachment
- 11 References
- 12 External links
Hedera is the generic term for ivy. The specific epithet helix derives from Ancient Greek "twist, turn" (see: Helix), and from the Latin helicem, "spiral-shaped," first used around 1600.<ref name=RHSLG>Template:Cite book</ref><ref>Template:Cite web</ref>
Synonyms include Hedera acuta, Hedera arborea ("tree ivy"),<ref>Bean, W. J. (1978) Trees and Shrubs Hardy in the British Isles Volume 2.</ref> Hedera baccifera, Hedera grandifolia,<ref>International Plant Names Index</ref> bindwood, and lovestone.
Hedera helix is an evergreen climbing plant, growing to Template:Convert high where suitable surfaces (trees, cliffs, walls) are available, and also growing as groundcover where no vertical surfaces occur. It climbs by means of aerial rootlets with matted pads which cling strongly to the substrate. The ability to climb on surfaces varies with the plants variety and other factors: Hedera helix prefers non-reflective, darker and rough surfaces with near-neutral pH. It generally thrives in a wide range of soil pH with 6.5 being ideal, prefers moist, shady locations and avoids exposure to direct sunlight, the latter promoting drying out in winter.<ref>Template:Cite web</ref>
The leaves are alternate, Template:Convert long, with a Template:Convert 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 Template:Convert 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 Template:Convert in diameter, ripening in late winter,<ref name=RHSAZ>Template:Cite book</ref> and are an important food for many birds, though somewhat poisonous to humans.
One to five seeds are in each berry, which are dispersed after being eaten by birds.<ref name="Metcalfe"/><ref name="McAllister"/><ref name="flora"/>
The three subspecies are:<ref name="Metcalfe"/><ref name="Ackerfield"/>
- H. h. helix
- central, northern and western Europe, plants without rhizomes, purple-black ripe fruit
- H. h. poetarum Nyman (syn. Hedera chrysocarpa Walsh)
- southeast Europe and southwest Asia (Italy, Balkans, Turkey), plants without rhizomes, orange-yellow ripe fruit
- H. h. rhizomatifera McAllister
- southeast Spain, plants rhizomatous, purple-black ripe fruit
The closely related species Hedera canariensis and Hedera hibernica are also often treated as subspecies of H. helix,<ref name="flora"/><ref name="Europe"/> though they differ in chromosome number so do not hybridise readily.<ref name="McAllister"/> 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.<ref name="flora"/><ref>The Holly and the Ivy. Shropshire Botanical Society Newsletter Autumn 2000: page 14</ref>
The northern and eastern limits are at about the Template:Convert winter isotherm, while to the west and southwest, it is replaced by other species of ivy.<ref name="Metcalfe">Template:Cite journal</ref><ref name="McAllister">Template:Cite journal</ref><ref name="flora">Flora of NW EuropeTemplate:Dead link</ref><ref name="Ackerfield">Ackerfield, J. & Wen, J. (2002). A morphometric analysis of Hedera L. (the ivy genus, Araliaceae) and its taxonomic implications. Template:Webarchive Adansonia sér. 3, 24 (2): 197-212.</ref><ref name="Europe">Flora Europaea: Hedera helix</ref><ref>Stace, C. A. & Thompson, H. (1997). New Flora of the British Isles. Cambridge University Press Template:ISBN</ref> Hedera helix itself is much more winter-hardy and survives temperatures of Template:Convert (USDA Zone 6a) and above.<ref>Template:Cite web</ref>
Cultivation and uses
The ivy 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.<ref name="Metcalfe"/><ref>Plant for Wildlife: Common Ivy (Hedera helix) Template:Webarchive</ref>
In Europe, it is frequently planted to cover walls<ref>Template:Cite web</ref> and the governmentTemplate:Which recommends growing it on buildings for its ability to cool the interior in summer, while providing insulation in winter, as well as protecting the covered building from soil moisture, temperature fluctuations and direct exposure to heavy weather.<ref>Template:Cite web</ref> Further uses include weed suppression in plantings, beautifying unsightly facades and providing additional green by growing on tree trunks.
However, ivy can be problematic. It is a fast-growing, self-clinging climber that is capable of causing damage to brickwork, guttering, etc., and hiding potentially serious structural faults, as well as harbouring unwelcome pests. Careful planning and placement are essential.<ref>Template:Cite web</ref>
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.<ref>NCCPG Plant Heritage: The common ivyTemplate:Dead link</ref>
- 'Angularis Aurea'<ref>Template:Cite web</ref>
- ’Buttercup’<ref>Template:Cite web</ref>
- 'Caecilia'<ref>Template:Cite web</ref>
- ’Ceridwen’<ref>Template:Cite web</ref>
- 'Congesta'<ref>Template:Cite web</ref>
- 'Duckfoot'<ref>Template:Cite web</ref>
- 'Glacier'<ref>Template:Cite web</ref>
- 'Goldchild'<ref>Template:Cite web</ref>
- ’Golden Ingot’<ref>Template:Cite web</ref>
- 'Manda's Crested'<ref>Template:Cite web</ref>
- 'Midas Touch'<ref>Template:Cite web</ref>
- 'Parsley Crested'<ref>Template:Cite web</ref>
- ’Shamrock’<ref>Template:Cite web</ref>
- 'Spetchley'<ref>Template:Cite web</ref>
Ivy extracts are part of current cough medicines.<ref>Template:Cite webTemplate:Dead link</ref> In the past, the leaves and berries were taken orally as an expectorant to treat cough and bronchitis.<ref>Bown. D. (1995). Encyclopaedia of Herbs and their Uses. Dorling Kindersley, London. Template:ISBN</ref> In 1597, the British herbalist John Gerard recommended water infused with ivy leaves as a wash for sore or watering eyes.<ref>Template:Cite book</ref> The leaves can cause severe contact dermatitis in some people.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> 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, ivy has predominantly been spread to areas by human action. 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.<ref>Oregon bans sale of English ivy, butterfly bushes</ref>
Having disappeared during the glaciation, ivy is believed to have been spread back across the continent by birds once the continent warmed up again.<ref>Template:Cite web</ref> With a great capacity for adaptation, ivy will grow wherever development conditions and habitat similar to that of its European origins exist, occurring as opportunistic species across a wide distribution with close vicariant relatives and few species, indicating recent speciation.
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.<ref>Template:Cite web</ref>
H. helix has been listed as an "environmental weed" by the Department of Conservation since 1990.<ref>Template:Cite book</ref>
In the United States, H. helix is considered weedy or invasive in a number of regions and is on the official noxious weed lists in Oregon and Washington.<ref name="USDA">USDA Plants Profile: Hedera helix</ref> 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.<ref name="nil">Template:Cite web</ref><ref name="Arlington">Controlling English Ivy Arlington County, Virginia Department of Parks, Recreation and Community Resources.</ref> Its sale or import is banned in Oregon.<ref>Controlling English Ivy Template:Webarchive. Northwest Coalition for Alternatives to Pesticides.</ref> Ivy can easily escape from cultivated gardens and invade nearby parks, forests and other natural areas.
Control and eradication
Ivy should not be planted or encouraged in areas where it is invasive. Where it is established, it is very difficult to control or eradicate. In the absence of active and ongoing measures to control its growth, it tends to crowd out all other plants, including shrubs and trees.
Damage to trees
Ivy can climb into the canopy of young or small trees in such density that the trees fall over from the weight,<ref name="Arlington"/> a problem that does not normally occur in its native range.<ref name="Metcalfe"/> 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.<ref name="Arlington"/>
Use as building facade green
As with any self-climbing facade green, some care is required to make best use of the positive effects: Ivy covering the walls of an old building is a familiar and often attractive sight. It has insulating as well as weather protection benefits, dries the soil and prevents wet walls, but can be problematic if not managed correctly.
Ivy, and especially European ivy (H. helix) grows vigorously and clings by means of fibrous roots, which develop along the entire length of the stems. These are difficult to remove, leaving an unsightly "footprint" on walls, and possibly resulting in expensive resurfacing work. Additionally, ivy can quickly invade gutters and roofspaces, lifting tiles and causing blockages. It also harbors mice and other creatures. The plants have to be cut off at the base, and the stumps dug out or killed to prevent regrowth.<ref>Template:Cite web</ref>
Therefore, if a green facade is desired, this decision has to be made consciously, since later removal would be tedious.
Mechanism of attachment
Hedera helix is able to climb relatively smooth vertical surfaces, creating a strong, long lasting adhesion with a force of around 300 nN.<ref>Template:Cite journal</ref> This is accomplished through a complex method of attachment starting as adventitious roots growing along the stem make contact with the surface and extend root hairs that range from 20-400 μm in length. These tiny hairs grow into any small crevices available, secrete glue-like nanoparticles, and lignify. As they dry out, the hairs shrink and curl, effectively pulling the root closer to the surface.<ref name=":0">Template:Cite journal</ref> The glue-like substance is a nano composite adhesive that consists of uniform spherical nanoparticles 50-80 nm in diameter in a liquid polymer matrix. Chemical analyses of the nanoparticles detected only trace amounts of metals, once thought to be responsible for their high strength, indicating that they are largely organic. Recent work has shown that the nanoparticles are likely composed in large part of arabinogalactan proteins (AGPs), which exist in other plant adhesives as well.<ref name=":1">Template:Cite journal</ref><ref name=":2">Template:Cite journal</ref> The matrix portion of the composite is made of pectic polysaccharides. Calcium ions present in the matrix induce interactions between carboxyl groups of these components, causing a cross linking that hardens the adhesive.<ref name=":1" />
- Hedera helix at Weedbusters (New Zealand)
- The Know Ivy League at the City of Portland, Park & Recreation Bureau website