Collector’s Choice: Cotinus obovatus

The Anacardiaceae is a fascinating plant family whose ornamental and culinary appeal is surpassed only by the misery it imposes on untold numbers every year. The source of the trouble is a phenolic compound known as urushiol, which causes poison oak, poison ivy, and poison sumac and is found in virtually all members of the family. Very little of the compound is necessary to wreak epidermal havoc, as aircraft mechanics who worked at the end of WWII can attest. The electrical system insulation in aircraft of those days used cardol, the fluid found in the fruit of the “type” genus of the family, Anacardium occidentale, the cashew, and the workers who maintained these early airplanes were rewarded for their efforts with painful lesions and blisters.

Although related to the cashew, members of the genus Cotinus pose little, if any, risk to gardeners. Chemical analysis would turn up traces of urshiol, but in insufficient quantity to affect any except those with severe sensitivity. The plants are far better known for their distinctive ornamental assets. Of the genus’s two species, the so-called European smoketree, Cotinus coggygria, is more familiar in Western horticulture, especially its purple-foliaged forms. It has a surprisingly wide range of natural distribution. I have observed this species in extremely parched sites in northeastern Turkey as well as under considerably more lush conditions in China’s Sichuan province.

The American species, Cotinus obovatus, native to rocky bluffs and woodlands of the southeastern states, has garnered much less attention. Plants grow to 25 feet or more with an open, upright habit and handsome gray bark that turns scaly with age. The wood produces a yellow dye, a fact that nearly led to the plant’s extinction during the Civil War when the Union’s trade embargo against the Confederacy triggered severe over-collection of the plant.

As with many members of the family, male and female flowers appear on separate plants of all Cotinus. These are presented in many-branched terminal panicles in mid- to late spring. Light purple fine hairs attached to these panicles create a billowy, diaphanous effect, inspiring the common name applied to both species.

The specific epithet of American smoketree refers to its obovate, or egg-shaped, leaves, which are papery in texture, grow to two-and-a-half by eight inches, and are presented in false whorls on the ends of the branches. The foliage emerges in spring an effulgent green, burnished with coppery hues that hint at its autumnal display. For several weeks in October and early November, the foliage blazes in sensational oranges, reds, and yellows.

Although the species occurs naturally in calcareous, alkaline soils, it responds equally well to slightly acidic soils. Once established it is quite drought tolerant, making it an ideal choice for poor, sharply drained soils. Though it grows well in light shade, its autumnal flaunt is more intense in full sun.

Perhaps because of the overall rarity of this plant, no selection work has been done, and no named cultivars exist. That said, perhaps the most popular smoketree in commerce is an English hybrid known as ‘Grace’, which results from a cross between C. coggygria and its American cousin. It is an extremely vigorous plant, producing robust stems to 15 feet in three years or less. The “smoke,” which appears in mid- to late summer, gives way to a splendid fire of fall foliage.

TYPE OF PLANT: deciduous tree FAMILY: Anacardiaceae ORIGIN: southeastearn United States HARDINESS: USDAZone 5; Sunset zones 1A, IB, A2, 1-2, FOLIAGE: obovate, to 2 in. long and 8 in. wide; excellent orange to red fall color FLOWERS: terminal panicles covered with long wispy hairs, creating a hazy silhouette SOIL: alkaline to slightly acidic, poor, sharply drained EXPOSURE: full

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