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A small group of evergreen climbers, the number of species in which is a matter of taxonomic judgement. Here five are recognised but of these one – H. canariensis – is treated as a subspecies of H. helix in Flora Europaea. On the other hand, Poyarkova, in Flora SSSR, recognises six species in the Soviet Union alone. The genus ranges from the Canary Islands and Madeira through Europe, Asia Minor, the Caucasus, the Himalaya, and thence to southern and Central China, Formosa, and Japan. It is absent from the New World in the wild (the Hedera quinquefolia of Linnaeus is the true Virginia Creeper, Parthenocissus quinquefolia (L.) Planch.). Some species of New Guinea and Queensland once placed in Hedera are now referred to the genus Kissodendron.
All the ivies resemble the common one in going through a more or less prolonged juvenile (non-fruiting) stage during which the stems climb or creep by holdfast roots and the leaves are arranged in one plane, forming a mosaic. At length the plant normally produces non-climbing fertile branches, on which the leaves are markedly different in shape from those of the sterile shoots, being unlobed or scarcely lobed, and are arranged spirally round the stem (as they are on seedling plants). A characteristic of the genus is the presence on the young growths and in the inflorescence of stellate hairs or of scales (or both together). The hairs consist of a short ‘stalk’ from the apex of which a number of branches radiate. The scales are essentially similar in structure, but are appressed to the surface that bears them, and the rays are partly or wholly fused. The flowers in Hedera are bisexual, arranged in umbels which are solitary or grouped into panicles. Fruit a drupe. For propagation, see H. helix.
The most valuable and up-to-date work on the genus is: G. H. M. Lawrence and A. E. Schulze, ‘The Cultivated Hederas’, in Gentes Herbarum, Vol. 6 (1942), pp. 105–73. Tobler’s work Die Gattung Hedera (1912) is still of interest. For Shirley Hibberd’s The Ivy, see under H. helix.
Since Volume II was published, a work of the very highest quality on the ivy cultivars has been published: Peter Q. Rose, Ivies, London, 1980. Some recent articles are referred to below.
An open-ground trial of ivies was planted in the Royal Horticultural Society’s Garden at Wisley in 1977 and judged two years later. Lack of room precluded their assessment as wall-climbers, but the trial was valuable in showing that many ivies usually seen as pot-plants are useful in the garden. The majority of those receiving awards are green-leaved varieties, for many variegated and golden-leaved sorts do not succeed on the ground, H. colchica ‘Dentata Variegata’ being a notable exception. An interesting comment on the trial by Peter Rose will be found in The Garden (Journ. R.H.S.), Vol. 105, pp. 378–83 (1980).
Regrettably, no mention was made in the main volume of the so-called ‘tree ivies’. When cuttings of the bushy, flowering state are rooted, the plants retain the adult habit and become sturdy, rounded bushes that flower freely. The misleading name tree ivy goes back to Loudon, who used it in reference to an adult form of the common ivy distributed by Loddiges as H. helix arborescens, and was later taken up by Hibberd in The Ivy. The more appropriate term ‘bush ivy’ was used by Hibberd for trained plants of juvenile ivies.