Plant 77

Acer carpinifolium Siebold & Zucc. (Sapindaceae)


Hornbeam-leaved maple

The word 'maple' conjures up an image of woody plants with leaves similar to those depicted on the Canadian flag. However, there is a small number of species of maple with very different looking leaves. The forms of these leaves have frequently been used by botanists who name plants (taxonomists), particularly if the leaves remind them of familiar plants; the plant's scientific name reflecting this similarity.

In 1845, the German physicians Philipp von Siebold and Joseph Zuccarini, who were also explorers of east Asian plants, named Japanese maples based on the similarities of their leaves to vines (Acer cissifolium), hawthorns (Acer crataegifolium) and hornbeams (Acer carpinifolium). Despite the superficial similarity of their leaves, Acer carpinifolium and hornbeam are readily distinguished even without flowers or fruits; maple leaves are arranged on stems opposite each other, whilst hornbeam leaves are arranged alternately. If one looks carefully at the base of the Acer carpinifolium leaf blade there is a fan of fine veins, similar to those in more familiar maple leaves.

Acer carpinifolium is an endemic tree commonly found in the understorey and mid-forest layers of Japanese temperate deciduous forests, 200 m to more than 1,300 m above sea level. Japan is a global plant diversity hotspot that has provided many plants to brighten gardens in the western hemisphere. The genus Acer comprises about 100 species. The vast majority of these species are from East Asia; approximately 15% of the world's Acer species are Japanese, and most of these have been introduced into cultivation.

Hornbeam-leaved maple was introduced from Japan to Britain in 1879 by the Englishman Charles Maries. Maries, one of numerous plant collectors, was employed by the nursery firm James Veitch & Sons of Chelsea to find new horticultural plants that could be sold to European gardeners. Offspring or clones of many plants introduced by Veitch's collectors are found in horticulture today. In cultivation, hornbeam-leaved maple is a compact tree, rarely achieving the height (up to 10 m) recorded in Japanese forests.

Despite its unusual foliage, handsome form and spectacular yellow autumn colour, Hornbeam-leaved maple remains a rare plant in cultivation. At least part of this rarity is because of the difficulty of getting viable seed.

Acer carpinifolium is dioecious, that is there are separate male and female trees. The greenish flowers are arranged in pendulous strings up to 15 cm long, and the female trees will produce two-winged 'helicopter' fruits.

Further reading

Renner SS et al. 2007. The evolution of dioecy, heterodichogamy, and labile sex expression in Acer. Evolution 61: 2701-2719.

van Gelderen DM et al. 1994. Maples of the World. Timber Press.

Stephen Harris