Immature inflorescenceBerriesStems with rootlets used to cling to walls and tree trunks
Hedera helix, thecommon ivy,European ivy,King's Choice ivy, or justivy, is aspecies offlowering plant in thefamily Araliaceae. It isnative to most of Europe and parts of western Asia. Ivy is a clingingevergreenvine that grows on tree trunks, walls, and fences in gardens, waste spaces, and wild habitats. Ivy is popular as an ornamental plant, but escaped plants have become naturalised outside its native range. Ivy has considerablecultural significance and symbolism.
Synonyms includeHedera acuta,Hedera arborea ('tree ivy'),[2]Hedera baccifera, andHedera grandifolia.[3] Other common names are bindwood and lovestone.
Hedera helix is anevergreen climbing plant, growing to 20–30 m (66–98 ft) high where suitable surfaces (trees,cliffs,walls) are available, and also growing asgroundcover where no vertical surfaces occur. It climbs by means ofaerial rootlets with matted pads which cling strongly to the substrate. The ability to climb on surfaces varies with the plants variety and other factors:H. helix prefers non-reflective, darker and rough surfaces with near-neutralpH. It generally thrives in a wide range ofsoil pH with 6.5 being ideal, prefers moist, shady locations and avoids exposure to direct sunlight, the latter promoting drying out in winter.[4]
Theleaves are alternate, 50–100 mm (2–4 in) long, with a 15–20 mm (0.6–0.8 in)petiole; they are of two types, withpalmately 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.
Theflowers are produced from late summer until late autumn, individually small, in 3-to-5 cm-diameter (1.2-to-2.0 in)umbels, greenish-yellow, and very rich innectar, an important late autumn food source for bees and other insects.
Thefruit are purple-black to orange-yellowberries 6–8 mm (0.2–0.3 in) in diameter, ripening in late winter,[5] and are an important food source for many birds.
One to fiveseeds are in each berry, which are dispersed after being eaten by birds.[6][7][8]
H. h. helix[10] - central, northern and western Europe, plants withoutrhizomes, purple-black ripe fruit,
H. h. poetarum Nyman (syn.Hedera chrysocarpa Walsh) (Italian ivy, poet's ivy) - southeast Europe and southwest Asia (Italy, Balkans, Turkey), plants without rhizomes, orange-yellow ripe fruit,
H. h. rhizomatifera McAllister - southeast Spain, plantsrhizomatous, purple-black ripe fruit.
The closely related speciesHedera canariensis andHedera hibernica are also often treated as subspecies ofH. helix,[8][11] though they differ inchromosome number and so do nothybridise readily.[7]H. helix can be best distinguished by the shape and colour of its leaftrichomes, usually smaller and slightly more deeply lobed leaves and somewhat less vigorous growth, though identification is often not easy.[8][12]
The genus nameHedera is theClassical Latin word for 'ivy', which is cognate with Greekχανδάνω (khandánō) 'to get, grasp', both deriving ultimately fromProto-Indo-European*gʰed- 'to seize, grasp, take'. Thespecific epithethelix derives fromAncient Greekἕλιξ (helix), 'helix', and from the Latinhelicem, 'spiral', first used around 1600. The binomial in its entirety thus has the meaning "the clinging plant that coils in spirals (helices)".[13][14][15]
The modern Englishivy derives from Middle Englishivi, from Old Englishīfiġ, deriving in turn from Proto-Germanic*ibahs. The meaning is uncertain, but the word may be cognate with theAncient Greekἴφυον (íphuon), referring to notHedera helix, but the unrelated English lavender, orLavandula angustifolia.[16]
The northern and eastern limits are at about the −2 °C (28 °F) winter isotherm, while to the west and southwest, it is replaced by other species of ivy.[6][7][8][9][11][18]Hedera helix itself is much more winter-hardy and survives temperatures of −23.3 °C (−9.9 °F) (USDA Zone 6a) and above.[19]
The Centre for Invasive Species Solutions listsHedera helix as a weed across southern, especially south-eastern Australia, and local councils provide advice on how to remove it and limited services for removal.[20] It is officially scheduled as a weed inWestern Australia and theAustralian Capital Territory.[20]Hedera helix is the only species of ivy bearing the legal status of 'declared weed' in Australia; however, it may be the case that much of what is identified as invasive "English Ivy" in Australia is in realityHedera hibernica.[20]
In theUnited States,H. helix is considered weedy or invasive in a number of regions and is on the officialnoxious weed lists inOregon andWashington, with its sale being banned in both states.[24][25][26][27] Like other invasive vines such askudzu,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 thePacific Northwest and theSouthern United States.[28][29] Ivy can easily escape from cultivated gardens and invade nearby parks, forests and other natural areas via squirrels and birds.[30]
Once ivy is established it is very difficult to control or eradicate. If left untreated it will crowd out other ground cover plants and can choke out and kill shrubs and overstory trees.[31]
Tested and successful methods of control are mechanical removal and chemical applications.[31]
Ivy can climb into the canopy of young or small trees in such density that the trees fall over from the weight,[29] a problem that does not normally occur in its native range.[6] 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.[29] It is also thought to be a reservoir forleaf scorch bacteria.[32] However, the UK Woodland Trust considers that it does not damage trees and hence does not require removal.[33] The ivy also blocks the sun from the trees that need it for photosynthesis.
Ivy is widely cultivated as anornamental 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.[6][34]
In Europe, it is frequently planted to cover walls[35] and the Bavarian government 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.[36] 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.[37]
Over 30cultivars have been selected for leaf traits such as yellow, white,variegated (e.g. 'Glacier'), and deeply lobed (e.g. 'Sagittifolia'), and other traits like purple stems and slow,dwarfed growth.[38]
Ivy berries are somewhat poisonous to humans, but extracts from ivy leaves are part of currentcough medicines.[56] A 2020 evidence review found thatH. helix preparations "may be a therapeutic option for treating early symptoms of respiratory tract infections", saying that "the best effectiveness forH. helix preparations has been proven for coughing, as an expectorant and to reduce the frequency and intensity of cough. Only weak evidence was found for all other researched symptoms."[57]
In the past, the leaves and berries were taken orally as anexpectorant to treat cough andbronchitis.[58] In 1597, the British herbalistJohn Gerard recommended water infused with ivy leaves as a wash for sore or watering eyes.[59] The leaves can cause severecontact dermatitis in some people.[60][61] People who have this allergy (strictly atype IV hypersensitivity) are also likely to react to carrots and other members of theApiaceae as they contain the same allergen,falcarinol.
Previous studies showed that theH. helix extract containsα-hederin and β-hederin, falcarinol, didehydrofalcarinol, rutin, caffeic acid, chlorogenic acid, emetine, nicotiflorin, hederasaponin B and hederacoside C.[62] However, only three extracted components were detectable more than 1.5% in the European ivy leaves (hederacoside C 15.69%, chlorogenic acid 2.07%, and rutin 1.62%). Other components were detectable in very few amounts (< 1%) or not detectable in some studies.[63]
Owing to the large number ofsaponins in the leaves and fruits ofH. helix, it is mildly poisonous to animals like rabbits and can lead toanemia.[64][65]
In a hunting session for resources, birds would restrict the number of ivy berries ingested because of the moderate toxicity. However, berries are taken in larger quantities in the spring once they have ripened and lost some of their toxicity.[66]
As with any self-climbingfaçade green, some care is required to make best use of the positive effects: Ivycovering the walls of an old green wall is a familiar and often attractive sight. It hasinsulating as well as weather protection benefits,[citation needed] dries the soil and prevents wet walls, but can be problematic if not managed correctly.
Hedera 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 invadegutters and roof spaces, 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.[67]
Hedera helix is able to climb relatively smooth vertical surfaces, creating a strong, long lasting adhesion with a force of around 300 nN.[68] This is accomplished through a complex method of attachment starting asadventitious roots growing along the stem make contact with the surface and extend root hairs that range from 20 to 400 μm in length. These tiny hairs grow into any small crevices available, secrete glue-likenanoparticles, andlignify. As they dry out, the hairs shrink and curl, effectively pulling the root closer to the surface.[69]
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 ofarabinogalactan proteins (AGPs), which exist in other plant adhesives as well.[70]
^Alkattan, A., Alameer, R., Alsalameen, E. et al. Safety of English ivy (Hedera helix) leaf extract during pregnancy: retrospective cohort study. DARU J Pharm Sci (2021).https://doi.org/10.1007/s40199-021-00415-7
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