A large and important genus composed chiefly of deciduous trees, some being of the largest size, many middle-sized or small, a few shrubby. The hardy species are widely spread over the three northern continents, the finest trees being natives of N. America. A large number come from E. Asia, many of which, however, are small trees.
The most constant and distinctive characters of the genus are the opposite leaves and the form of the fruits. Each fruit consists normally of two sections, known as samarae (commonly as ‘keys’), attached to each other by their bases, and each ‘key’ consists of a nutlet, containing one, sometimes two, seeds, and a large, thin, membranous wing. These wings assist in the dispersal of the seed. The flowers are sometimes unisexual. The typical maple leaf is broad and flat, with five palmate lobes. But there is a great diversity of shape in the genus: some species have as many as eleven or thirteen lobes to each leaf, many have but three lobes, and there is a distinct group with leaves not lobed at all. Finally comes the section of maples with compound leaves consisting of three or five distinct leaflets, sometimes kept genetically separate as Negundo.
Most of the maples have tamely coloured flowers, varying from yellow to greenish white; a few have purple flowers (like A. circinatum), and are very ornamental when in blossom; whilst others, like A. opalus, flower in early spring before the leaves expand, and although not highly coloured make, at that season especially, a pleasing display. Still, on the whole, the attractions of the maples generally are in the large or handsomely cut foliage, and in the red or yellow tints many of them assume in autumn.
Few trees are more easily cultivated than these, their chief requirements being a rich moist soil and a moderately sunny, or at any rate not unduly shaded, position. Some of the smaller species, however, like A. rufinerve, A. capillipes, and A. argutum, like their stems shaded. All the maples should, if possible, be raised from seeds; if grafting has to be resorted to, as for the numerous coloured-leaved and variously habited varieties, the scions should be worked on stocks of their own species.
The number of species of maple has so largely increased in this century by introductions from China that even the largest garden could not accommodate them all, though no other genus of hardy broad-leaved trees is so varied or has so many species that are worthy of cultivation. The following is a short selection:
Large and Medium-sized Trees: A. cappadocicum ‘Aureum’, ‘Rubrum’ and var. sinicum; A. heldreichii; A. lobelii; A. monspessulanum; A. opalus; A. platanoides, A. p. ‘Goldsworth Purple’, ‘Crimson King’ or ‘Faasen’s Black’, A. p. ‘Drummondii’; A. pseudoplatanus ‘Atropurpureum’ (syn. ‘Purpureum Spaethii’); A. rubrum; A. saccharum; A. saccharinum (but the brittle wood makes it unsuitable for town-planting); A. trautvetteri; A. × zoeschense.
Small Trees and Shrubs: A. argutum; A. circinatum; A. cissifolium; A. davidii; A. forrestii; A. griseum; A. grosseri var. hersii; A. japonicum, A. j. ‘Aureum’ and ‘Vitifolium’; A. negundo and its cultivars; A. nikoense; A. palmatum and its cultivars; A. pensylvanicum; A. pseudoplatanus ‘Brilliantissimum’; A. rufinerve; A. triflorum.
From the Supplement (Vol. V)
It was remarked on page 185 that ‘no other genus of hardy broad-leaved trees is so varied or has so many species that are worthy of cultivation.’ Fifty-four pages were devoted to describing those in cultivation, but many more would have been needed to do full justice to the genus had the treatment been prepared at the present time. This is largely thanks to the new introductions by Gordon Harris, who has built up a remarkably comprehensive collection of maples at Mallet Court in Somerset, which includes numerous cultivars of A. palmatum previously unknown in this country. Most of these are mentioned in this supplement.
It is indisputable that many species recognised in the present edition are closely related to others named earlier and merit only subspecific rank. The relevant synonyms are added in this supplement, but it must be emphasised that not all the new combinations made by Dr Murray would necessarily be accepted by other botanists working on the genus, though the majority probably would be.
Recent Literature
(I.D.S.Y.B. International Dendrology Society Year Book)
Banks, R. A. – ‘Some Maples at Hergest Croft, Herefordshire’, I.D.S.Y.B. 1971 pp. 8-13.
de Jong, P. C. – ‘Flowering and Sex Expression in Acer L.’ Medel. Landbouwhogeschool, Wageningen, No. 76-2 (1976). An important contribution to our knowledge of the genus, with a proposed classification.
Harris, J. G. S. – ‘Maples in my Garden’, I.D.S.Y.B. 1971, pp. 14-23.
Harris, J. G. S. – ‘Maples in Taiwan and Hong Kong’, I.D.S.Y.B. 1972, pp. 59-62.
Harris, J. G. S. – ‘Propagation of Acers’, I.D.S.Y.B. 1973, pp. 57-61.
Harris, J. G. S. – ‘Maples from Japan’, Journ. R.H.S., Vol. 199, pp. 394-9 (1974).
Harris, J. G. S. – ‘Growing Maples from Seed’, The Garden (Journ. R.H.S.), Vol. 101, pp. 503-6 (1976).
Harris, J. G. S. – ‘Japanese Maples’, The Plantsman, Vol. 3, pp. 234-50 (1982).
Harris, J. G. S. – ‘An Account of Maples in Cultivation’, The Plantsman, Vol. 5, pp. 35-58 (1983).
Lamb, J. E. D., and Nutting, F.J. – ‘Propagation Techniques in the Genus Acer’, The Plantsman, Vol. 5 (3), pp. 186-92 (1983).
Lancaster, Roy – ‘Maples of the Himalaya’, The Garden (Journ. R.H.S.), Vol. 101, pp. 589-93 (1976).
Mulligan, B.O. – ‘Maples in the North Western U.S.A.’, I.D.S.Y.B. 1970, pp. 13-19.
Murray, Edward A. – The author, a leading authority on the genus, has published numerous notes, keys and new combinations in his cyclostyled publication Kalmia.
Ogata, Ken – A Dendrological Study on the Japanese Aceraceae … Inst. For. Bot., Univ. of Tokyo (1965).
Vertrees, J.D. – Japanese Maples. Timber Press, Forest Grove, Oregon, USA (1978). See further under A. palmatum.