Once a magnificent shade tree in the woodlands of eastern North America, the introduction of an Asian plant fungal disease devastated populations of native American chestnut trees. Thus, the Chinese chestnut's better resistance to this disease finds it grown as a substitute tree, while the American chestnut grows only as a leggy shrub that rarely flowers or sets fruits.
Both members of the beech family (Fagaceae), these two tree species are closely related and grouped into the botanical genus Castanea. The American chestnut is known as Castanea dentata, whereas the Chinese chestnut species is known as Castanea mollissima.
American chestnut hails from the eastern deciduous and mixed forests of eastern North America–from New England southwestward across southernmost Ontario and the Appalachians to central Mississippi State. Chinese chestnut is native to eastern Asia–from the Korean Peninsula westward across the northern provinces of China.
History in North America
In 1904 a young Chinese chestnut tree was introduced into North America in New York that was infected with the chestnut blight fungus (Cryphonectria parasitica). In the 1930s and 1940s, the majority of American chestnuts were exposed to this fungus and died back to their trunk stumps. While the Chinese chestnut species demonstrated some natural resilience to the fungus, the American chestnut had absolutely none. As fewer American chestnuts survived, few seeds were made–eventually severely diminishing the species. The Chinese chestnut could be a substitute shade tree, but horticulturists selected varieties with seemingly better resilience to the fungus now widespread across North America.
The American chestnut today rarely grows as an upright, narrowly oval, large-canopied tree like it did before introduction of the chestnut blight fungus. Plants encountered are no taller than 20 feet–with many thin upright branches sprouting from old tree trunks, from just below the area infected by the fungus. The narrow oval leaves are kelly green and tapering ovals with large-toothed edges. Undersides of leaves are smooth. Rarely do the male catkin flowers and female blossoms at the base of the catkins form on these young branches in early summer. Thus, the spined green-turning-brown fruits with deliciously sweet meaty nuts are rarely produced anymore.
Chinese chestnut grows 40 to 60 feet tall and nearly as wide in its leafy canopy. The leaves are deep glossy green with teeth on the edges. Leaf undersides are lightly hairy. In early summer, male flowering catkins release a foul odor and shed pollen to reach the female flowers on branch tips. Round, spiny fruits mature from green to brown and split open to release edible nuts that are not as sweetly delicious as those of the American chestnut.
With the presence of the fungus across both Asia and North America, the American chestnut is no longer planted and usually never seen as a stately specimen tree. The Chinese chestnut is used as a substitute for the American chestnut, becoming a shade tree for large landscapes. The Chinese species is not used as a residential or street tree because of the smell of the flowers and the fruit, nut and leaf litter shed annually. However, it is valuable in difficult, urban locations where a shade tree is needed to grow in a dry, hot or slightly alkaline soil situation.
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