Ivy (Hedera helix, Araliaceae, the ginseng family) is native in the UK and is very widespread in North Somerset, coming second only to nettles in geographical distribution. The name Ivy comes from the Old English ‘Ifig’ meaning bitter, referring to the taste of the berries. It is highly adaptable, growing on walls, up trees and often as ground cover, frequently in situations of low light intensity and low nutrient status. It may suppress the ground flora, and sometimes good management may indicate that it could be reduced to benefit biodiversity. It is not usually necessary to remove Ivy from trees, unless the growth makes the tree top-heavy and liable to windthrow. The evergreen leaves are unlobed on flowering shoots and typically bear three or five lobes on vegetative shoots. The fertile shoots that are produced in situations of high light intenstiy lack the adhering rootlets and tend to project at right angles to a supporting tree. The leaves are eaten by horses, deer, sheep and cattle.
Despite the perception of the general public, Ivy is not parasitic, and it uses its stem roots merely to adhere to walls and the trunk of trees. The flowers are used as food by the autumn brood of the Holly Blue butterfly. I have watched these butterflies laying eggs on the Ivy in my own garden. Ivy berries also provide food for many birds throughout the winter, when it is an ideal roost for birds and many invertebrates. In the Autumn it produces flowers that are rich in nectar and that attract many insects, particularly hoverflies and wasps. There are now many ornamental varieties, grown decoratively in our gardens where it is also useful for ground cover. The leaves are rich in terpenoids, and are not attractive to slugs. The leaves and fruits contain the saponic glycoside hederagenin which, if ingested, can cause breathing difficulties and coma. The sap can cause dermatitis with blistering and inflammation. This is apparently due to the presence of polyacetylene compounds
There are two native subspecies in the UK – ssp helix ans ssp hibernica the latter originating in Ireland and found more frequently in the west of North Somerset. They are not easily distinguished . The subspecies hibernica has hairs that are pale yellowish brown with some leaves greater than 8cm across and lobed less than half way to the base. The subspecies helix has whitish hairs, leaves often less than 8 cm across with lobes more than halfway to the base. Ssp. hibernica probably arose in Ireland as a tetraploid, with double the normal number of chromosomes. Orobanche hederae the Ivy Broomrape, a leafless plant that grows as a parasite of Ivy and which is found in several parts of Nailsea including my own garden, is said to favour the ssp hibernica.
If you happen to look up Ivy on the international web, you will find that many of the references give advice on ‘how to eliminate English Ivy from your garden’. Ivy was introduced into the United States and now grows particularly well in the East and West coastal states, and it also flourishes in Australia and New Zealand This is rather like the situation with Purple Loosestrife, a very attractive plant seen occasionally in damp situation in the United Kingdom, but which has taken over large areas of wilderness in the USA since there appears to be no natural means of controlling it there. This shows how careful we must be in transferring alien plants to new territories.