Lesser-known species offer hardiness as well as beauty of leaf and bark
BY DANIEL J. HINKLEY
PHOTOGRAPHY BY LYNNE HARRISON
EARLY IN MY HORTICULTURAL youth, I developed a fondness for the genus Acer—the maples—by learning to identify the species native to the uplands of northern Michigan. This infatuation became an affaire du coeur that continued into graduate school, where I devoted my thesis to this diverse assemblage of highly ornamental, durable, long-lived species, which occur throughout the Northern Hemisphere. Later, I would have the opportunity to observe and collect seed of numerous maple species in the mountains of Nepal, Japan, Korea, China, Turkey, Taiwan, and even northern Vietnam.
Though there are 13 species of maples native to North America, the geographic center of the genus is Asia, with over 100 species. From this sizable group the discerning North American gardener can select a large number of little known, hardy, distinctive, small to moderate-size trees that offer handsomely textured summer foliage, fiery autumn color, and, frequently, startling striped or exfoliating bark.
THREE CHOICE SPECIES
With its scores of first-class cultivars, the Japanese maple, A. palmatum, has already achieved superstardom. Indeed, there is hardly a more suitable tree for small gardens in USDA Zones 6 through 10. However, there are many other gardenworthy Asian species that deserve wider use, some of them ideally suited to those who garden in more climatically challenged areas.
For summer foliage with undiluted dazzle, few small trees can compete with A. shirasawanum ‘Aureum’, known commonly as the golden full moon maple. A close ally of the Japanese maple, this species used to be known as A. japonicum ‘Aureum’. By any name, it offers the gardener superb effects, with rounded, many-lobed, burnished gold foliage held densely on a globe-shaped tree that grows slowly to 20 by 20 feet or slightly more. Although the color achieves its most refulgent effects in full sun, the leaf edges have a tendency to burn, so I cultivate it in light shade, where the tone mellows to a paler yellow. It makes a good selection for Zones 6 and above.
Acer pseudosieboldianum, from the mountains of Korea, offers the ornamental characteristics of A. palmatum while surviving temperatures to -20°F. The dark green, orbicular, sharply lobed leaves, borne on a rounded framework rising to 30 feet, take on brilliant tints of claret and scarlet in autumn. The jade-green branches and finely textured silhouette of this maple are an elegant addition to the landscape in winter, becoming even lovelier when they hold drops of rain or a tracery of snow.
Equally tolerant of the brutal climatic extremes of middle American gardens is A. truncatum, the so-called Shantung maple. Native to the high steppes of northern China, it forms a handsome mounded specimen to 30 by 30 feet, cloaked with orbicular, lobed, glossy green foliage that emerges in spring with an overtone of purple. In autumn, the foliage assumes intense, varnished shades of orange and red. A zippy, vigorous, variegated form, A. truncatum ‘Akikaze Nishiki’, offers foliage brightly splashed in white. Both ‘Akikaze Nishiki’ and the plain species deserve to be grown much more widely, especially in Zones 4 through 10.
LEAVES WITH A DIFFERENCE
The typical multilobed maple leaf is not characteristic of numerous Asian species. With their very un-maple-like appearance, these species contribute a singular texture to the garden while providing an opportunity to test the identification skills of your fellow gardeners. A case in point is the hornbeam maple, A. carpinifolium (opposite), which carries pairs of narrow, lance-shaped leaves that perfectly mimic those of the European hornbeam, Carpinus betulus. In autumn, they ripen to a brilliant yellow. Despite having studied the genus in depth, I experienced a high level of befuddlement when I encountered this species for the first time in the mountains southwest of Tokyo. The hornbeam maple ultimately forms a handsome, rounded specimen to 20 by 15 feet, and is ruggedly hardy, to Zone 3.
The hawthorn maple, A. crataegifolium, a small tree or large shrub to 15 feet, poses its own foliar puzzles, bearing small, triangular, slightly lobed leaves of bluish green held along handsome young stems of purple red. This species also hails from the mountains of Japan, where it occurs primarily in shaded conditions—an environment it prefers in cultivation. The sprightly variegated clone, A. crataegifolium ‘Veitchii’, presents an irregular play of creamy white in the leaves, which makes it particularly useful for brightening a gloomy shaded site. Hardy in Zones 6 to 10, it’s one of the most asked-about trees in our woodland garden at Heronswood.
Acer crataegifolium is one of several species known collectively as the stripebark or snakebark maples. While the new growth of these species is deep purple or bright red, the older wood develops startling green and white striations that enliven the garden during the winter months. (This effect, by the way, diminishes if the trees are planted in full sun, which causes the bark to scald and discolor.) When one considers that ornamental bark is the only characteristic of a deciduous tree that can be appreciated year round, its value becomes apparent.
In my estimation, the best of the lot is A. tegmentosum, a rounded tree growing to 30 feet that is native to Korea and Manchuria—areas with notably frigid winters. The bark, which displays fine, brilliant white striations against a green background, is unmatched by any other species of tree, and glows when illuminated by the low, slanting rays of the winter sun. The broad, papery leaves emerge a resplendent green in early spring and change to a rich lemon yellow in autumn before falling. As might be expected, the Manchu-stripe maple, as it is commonly called, is extremely hardy and will thrive in Zones 4 through 10.
Two other Asian maples offer outstanding bark, though in a manner decidedly different from the snakebark species. Acer griseum, the paperbark maple, is in a perpetual process of shedding its crisp, copper-colored shards of translucent skin. The compound foliage is made up of three leaflets (the specific epithet griseum comes from the ashen-gray color of their undersurface). If the tree is grown in full sun, the foliage
becomes a panoply of oranges and clarets in autumn before falling. I consider it to be one of the best year-round small trees one can cultivate in Zone 5 and above.
Much less well known is A. caudatum, with boldly serrated five-lobed leaves to four inches across held along an upright trunk, growing to 30 feet, that displays a striking overlay of crispy amber bark. When I first encountered this maple in eastern Nepal, at elevations of 10,000 to 12,000 feet, my immediate reaction was that I’d come across the Himalayan birch, Betula utilis. In autumn the foliage develops excellent tones of orange and red; the tree itself is hardy in Zones 4 through 10.
One by one, over many years, I have become acquainted with the Asian counterparts of the trees that surrounded our family farm in Michigan. With each new encounter, I become more aware of the enormous yet untapped horticultural potential of this genus. The attractions that maples offer are as numerous and diverse as the climates to which they are adapted. H
For sources of featured plants, turn to page 76.