European smoke tree (Cotinus Coggygria)
Lining walkway south of the Steam Plant
More of a large shrub than a tree, the leaves are long round ovals with a waxy sheen. Its most attractive feature is the appearance of its spent flowers, which in mid-summer envelop the plant in a wispy, grayish pinkish yellow "cloud" that, to an active imagination, resembles smoke. Large examples in the wild top 40 ft. in height, so ours ought to be able to attain the sacred 13 ft. eventually.
To visitors from the desert southwest the name "smoke tree" conjures up a gaunt, misshapen grayish-green apparition desperately clinging to life in a dry wash. That is Dalia spinosa, which never could survive the rigors of a moist, cool, well-cultivated university arboretum. Our smoke tree is totally unrelated. It originated in Europe, where it has been common in gardens for centuries. It was introduced into North America in the late 18th century, and has been widely disseminated. Its fall colors also can be worthwhile.
But back to the question: tree or shrub? Several authorities state that, unless artfully and persistently pruned, Cotinus Coggygria will remain low and bushy.
See Cotinus Coggygria on Wikipedia.