Acer L.

Family

Sapindaceae (formerly Aceraceae)

Common names

Maples

Article sources

New Trees

Bean

Acer is one of the most significant tree genera of the northern hemisphere. The 156 species occur in North America south to Mexico, in Europe and North Africa, and from the Middle East through the Himalaya to southeastern Asia (de Jong 2002). Though it is primarily a temperate genus, species of Acer occur in tropical Asia, crossing the equator on Java. They are trees or shrubs, grown primarily for their leaves, which display an array of shapes, sizes and colours. Bark is extremely variable and often diagnostic; it may be smooth, ridged or flaky, seldom rough or forming plates, an exception being the coarse exfoliating plates of A. yui. Bud scales are often large and foliose with 2–15 pairs, eventually caducous. The leaves are deciduous or evergreen, opposite and typically palmate with five lobes, although they may be entire or with 3–13 lobes, or they may be pinnate with three, five or rarely seven leaflets. Hairs are usually present in the vein axils of the leaf undersides and often elsewhere. Stipules are absent (present in A. saccharum subsp. nigrum). Inflorescences are extremely variable in form – compound or simple, corymbose, paniculate, racemose or umbellate – and are produced in terminal and/or lateral positions. Flowering occurs before or as the leaves emerge. The flowers are hermaphrodite or unisexual (trees sometimes dioecious). They have (four to) five (to six) sepals, (four to) five (to six) petals (rarely none), the sepals and petals sometimes fused together, usually yellowish or green, though some species have contrasting white petals and green or red sepals; (4–)8(–13) stamens, nectaries forming a fleshy disc or ring in the centre of the flower; the stamens may be inserted inside or outside the ring or, more commonly, emerge from the ring itself. The fruit is a two-seeded schizocarp, a dry indehiscent structure that breaks up at maturity into single-seeded sections. These sections each have a single wing and are known as samaras (van Gelderen et al. 1994, de Jong 2002). Development of the samara proceeds directly after flowering, and large but immature fruits are often a conspicuous feature of the trees through the summer. In the following account the entries for fruiting time refer to ripening.

Despite the interest of horticulturists, Acer has not been a subject for recent academic botanical study, and a modern revision is urgently needed to clarify the systematic position of many taxa. The taxonomy in this account is generally based on Piet de Jong’s classification in the current standard reference Maples of the World (van Gelderen et al. 1994), although this differs in some respects from other major authorities such as the recently available Flora of China account (Xu et al. 2008); some modifications have been included in the present work on the advice of Peter Gregory, in advance of his own forthcoming book on maples (Gregory, in prep.). A summary table of the infrageneric classification of Acer is provided below, which helps place un familiar species with better-known relatives, but for more detail Maples of the World should be consulted. A number of familiar species with multiple subspecific taxa are included, as some of the names are unfamiliar and represent recent collections. For these species simple keys covering the important characters are provided. Almost all species mentioned in this account are illustrated (mostly by colour photographs) in Maples of the World, its companion volume Maples for Gardens (van Gelderen & van Gelderen 1999), and An Illustrated Guide to Maples (le Hardÿ de Beaulieu 2003).

ACER L.

A guide to the infrageneric classification of Acer (derived from van Gelderen et al. 1994)

Section Parviflora

Leaves 3- (sometimes 5- or 7-) lobed, or simple

Bud scales 2- (sometimes 3-) paired

Inflorescence a large corymb

Flower 5-merous

Series Parviflora (e.g. A. nipponicum)

Leaves 3- or 5-lobed

Inflorescence paniculate-corymbose, with 35-400 flowers

Series Distyla (e.g. A. distylum)

Leaves simple

Inflorescence erect, with 35–70 flowers

Series Caudata (e.g. A. caudatum)

Leaves 3-, 5- or 7-lobed

Inflorescence erect, with 50–200 flowers

Section Palmata

Deciduous to evergreen

Leaves 3- to 13-lobed, or simple

Bud scales 4-paired

Inflorescence a terminal or occasionally axillary corymb

Flower 5-merous

Series Palmata (e.g. A. palmatum, A. japonicum)

Leaves 5- to 9- (to 13-) lobed

Inflorescence with 5–25 flowers

Series Sinensia (e.g. A. campbellii)

Leaves 3- to 7-lobed

Inflorescence large, elongated, 20–250 flowers

Series Penninervia (e.g. A. laevigatum)

Often almost evergreen

Leaves simple, leathery in texture

Inflorescence large, elongated, 20–250 flowers

Section Wardiana (e.g. A. wardii)

Leaves 3-lobed

Bud scales 2-paired

Inflorescence an upright corymb

 

Section Macrantha (e.g. A. pensylvarticum, A. davidii)

Bark often longitudinally striated (‘snakebark’)

Leaves simple or 3- to 7-lobed

Bud scales 2-paired

Inflorescence a terminal or occasionally axillary

raceme or corymb

Flower 5-merous

 

Section Glabra

Leaves simple or 3- to 5-lobed

Bud scales 2- to 4-paired

Inflorescence a terminal or axillary raceme or corymb, small

Flower 4- or 5-merous

Series Glabra (e.g. A. glabrum)

Monoecious

Leaves 3- to 5-lobed or partially trifoliolate

Flower 5-merous

Series Arguta (e.g. A. stachyophyllum)

Dioecious

Flower 4-merous

Section Negundo

Leaves compound, with 5–7 leaflets

Bud scales 2- to 3-paired

Inflorescence a raceme or compound raceme, with 15–50 dioecious flowers

Flower 4-merous

Series Negundo (e.g. A. negundo)

Leaves pinnate

Bud scales (2- to) 3-paired

Flowers apetalous, on long, pendulous peduncles, appearing before leaves

Series Cissifolia (e.g. A. cissifolium)

Leaves trifoliolate

Bud scales 2-paired

Flowers with petals, on long racemes, appearing with leaves

Section Indivisa (e.g. A. carpinifolium)

Leaves simple, with strongly parallel lateral veins

Bud scales 9- to 13-paired

Inflorescence terminal or axillary, with 10–20 flowers

Flower 4-merous

 

Section Acer

Leaves 3- to 5-lobed

Bud scales 5- to 13-paired

Inflorescences terminal or axillary corymbs

Flower 5-merous, but stamens usually 8

Series Acer (e.g. A. pseudoplatanus)

Leaves usually 5-lobed

Bud scales 5- to 10-paired

Inflorescence with 25–150 flowers

Series Monspessulana (e.g. A. monspessulanum)

Leaves usually 3-lobed, sometimes simple or 5-lobed

Bud scales 8- to 12-paired

Inflorescence with 10–50 flowers on pendulous pedicels

Series Saccharodendron (e.g. A. saccharum)

Leaves 3- to 5- (to 7-) lobed

Bud scales 6- to 9-paired

Inflorescences terminal, or axillary from leafless buds, 10–60 flowers on pendulous pedicels

Section Pentaphylla

Often evergreen, sometimes deciduous

Leaves simple or 3-lobed, sometimes compound

Bud scales 4- to 8-paired

Inflorescence a terminal or axillary corymb, with 25–75 flowers

Flower 5-merous

Series Pentaphylla (e.g. A pentaphyllum)

Leaves 5- to 7-lobed

Series Trifida (e.g. A. buergerianum)

Leaves usually more or less evergreen, simple to 3-lobed

Section Trifoliata

Leaves 3-foliolate

Bud scales 11 - to 15-paired

Inflorescence terminal or axillary, usually with 3 flowers, sometimes up to 25, in racemes or corymbs

Flower 5- or 6-merous

Series Grisea (e.g. A. griseum)

Often with peeling bark

Series Mandschurica (e.g. A. mandschuricum) Bark not peeling

Section Lithocarpa

Leaves large, 3- to 5-lobed

Bud scales 5- to 12-paired

Inflorescence axillary from leafless buds, racemose or corymbose with 10–20 flowers

Flower 5-merous

Series Lithocarpa (e.g. A. sterculiaceum)

Petioles sometimes lactiferous

Bud scales 8- to 12-paired

Inflorescences axillary from leafless buds, racemose or corymbose with 10–20 flowers

Series Macrophylla (e.g. A. macrophyllum)

Leaves deeply 5-lobed, with lactiferous petioles

Bud scales 5- to 8-paired

Inflorescences large, with 30–80 flowers in a corymbose panicle

Section Platanoidea (e.g. A. platanoides)

Leaves 3- to 7-lobed, occasionally simple, petioles lactiferous

Bud scales 5- to 8-paired or 6- to 10-paired

Inflorescence a terminal or axillary corymb

Flower 5-merous

 

Section Pubescentia (e.g. A. pilosum)

Leaves 3-lobed, glaucous below

Bud scales 6- to 10-paired

Inflorescence a terminal or axillary corymb

Flower 5-merous

 

Section Ginnala (e.g. A. ginnala)

Leaves simple or 3-lobed

Bud scales 5- to 10-paired

Inflorescence a terminal or axillary corymb

Flower 5-merous

 

Section Rubra (e.g. A. rubrum)

Leaves 3- to 5-lobed, glaucous below

Bud scales 4- to 7-paired

Inflorescence a cluster of 5 flowers from axillary buds

Flower 5-merous

 

Section Hyptiocarpa (e.g. A. laurinum)

Evergreen

Leaves simple, margins entire, glaucous below

Bud scales 7- to 11-paired

Inflorescence an axillary corymb or raceme

Flower 5-merous

From Bean's Trees & Shrubs

Acer

Maple

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, KenA 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.

Click on the images for a larger view.

‘It is a truth universally acknowledged …’ This male Acer sinopurpurascens at Arboretum Trompenburg is certainly in need of a wife (see p. 110). It is easy to forget how attractive the flowers of maples can be. Image J.R.P. van Hoey Smith.

Acer ceriferum (section Palmata, series Palmata), showing hairs in the axils of the veins on the underside of the leaves. Image P. Banaszczak.

Autumnal colours in Acer sieboldianum are as good as in any other maple, making it a most desirable small tree. Image J.R.P. van Hoey Smith.

Acer tonkinense probably needs a mild, sheltered garden to thrive, or to be maintained under glass. This young plant was photographed at the Esveld nursery, Boskoop. Image J.R.P. van Hoey Smith.

A fruiting shoot of Acer caudatifolium at Kew, grown from ETOT 54. Image T. Kirkham.

The bark of Acer caudatifolium has a sinuous pattern in shades of green, interspersed with many pale lenticels. Image R. Hitchin.

The evergreen Acer coriaceifolium is marginally hardy in much of our area, but flourishes at Hack-falls, New Zealand, where this picture was taken. Image J.R.P. van Hoey Smith.

The new growth of many maples flushes reddish or bronze, as here on a young Acer elegantulum at Plantentuin Esveld. Image J.R.P. van Hoey Smith.

The spring flush of a most un-maple-like maple. Grown and photographed as Acer laurinum, this is in fact A. pinnatinervium (see p. 100). Image J. Grimshaw.

Mature trunks of Acer longipes subsp. longipes in Sichuan, showing its rugged bark. Image T. Kirkham.

Attractive glossy foliage is produced by the slow-growing Acer monspessulanum subsp. turcomanicum. Image P. Banaszczak.

The contrast between the glaucous stems and bright red petioles of Acer negundo subsp. mexicanum adds a new twist to a familiar species. Image N. Macer.

The elegant foliage of Acer oliverianum subsp. formosanum emerges very early in the season. Image P. de Spoelberch.

Acer pictum subsp. okamotoanum dominates in this woodland on the Korean island of Ullung-do, where it is endemic. Image T. Kirkham.

Broad leaves with long-tipped lobes are characteristic of Acer pictum subsp. okamotoanum. Image R. Hitchin.

Acer pseudosieboldianum subsp. pseudosieboldianum is a good choice for those seeking striking autumnal colour in areas too cold for A. palma-tum. Image P. Banaszczak.

Of exceptional foliar beauty, Acer pseudosieboldianum subsp. takesimense is the second endemic maple of Ullung-do, once known as Takeshima Island. Image P. Banaszczak.

Acer pubinerve (syn. A. wuyuanense) is forming attractive small trees in those gardens fortunate enough to possess it. This one is in the US National Arboretum. Image J. Grimshaw.

Acer pycnanthum at Herkenrode. The autumnal colour is not as intense in cultivation as it is in the wild. Image P. de Spoelberch.

Fallen leaves of Acer pycnanthum reveal their autumn colours and glaucous undersides. Image P. de Spoelberch.

The generally reddish tint seen in Acer rubescens does not appear in the bark, but is apparent here in the petioles of the leaves in the background. Image R. Hitchin.

The pale glaucous leaf undersides of the Mexican Acer saccharum subsp. skutchii are distinctive. It is almost evergreen where winters are not severe. Image M. Foster.

The solitary female specimen of Acer sinopurpurascens at Rogów never sets viable fruit. Image P. Banaszczak.

Long drip-tips give an indication of the dampness of the natural habitat of Acer wardii, seen here in the Gongshan, Yunnan. Image M. Foster.

Acer capillipes

Acer forrestii

Acer macrophyllum

Acer spicatum

Species articles