Background

Ailanthus, tree of heaven, paradise tree, or tree of hell (as many like to call it) is an invasive tree across the United States, Canada, and Mexico. First introduced as an ornamental in the Eastern US and brought to California during the gold rush. This tree is common in urban areas and very tolerant of pollution and poor soil conditions. You can see tree of heaven in many mining towns in Arizona, some say it is holding up the old copper mining town of Jerome.

In Phoenix I’ve come across ailanthus in older neighborhoods and I can see its invasive nature by the numerous amount of small trees and sprouts surrounding the larger trees. Tree of heaven is dioecious (trees are either male or female), the male flowers have a very offensive odor. Crushed leaflets smell like peanuts to some.

The numerous seeds produced by ailanthus are only viable for 1 year and they spread by wind, water, birds, and humans. Established trees have long shallow lateral roots that sprout prolifically, often more so when the tree is disturbed. The sprouts grow very fast and have been recorded to grow 1” per day (Harlow, et al). Control is very difficult and usually a combination of cut stump treatment and foliar sprays are needed.

Identification

Tree of heaven has large alternate compound leaves (1’ to 3’ long) with 11 to 41 alternating leaflets. Leaflets are lanceolate with a pointed tip and they have 1 to 5 teeth at the base, but the sides and tip of the leaflet margin are smooth. The fruit is a twisted samara 1 to 1 ½” long, with the seed in the center. The twigs are thick and younger stems have many lenticels (raised spots on stem or twig that act as a spore) on the reddish-brown stem. These thick twigs are usually how I spot a tree of heaven, and I look for the large shield-shaped leaf scar. The bark varies and can be smooth to riged, sometimes appearing gray with lighter colored stripes.

Trees often mistaken for tree of heaven are pecan (Carya illinoensis) or smooth sumac (Rhus glabra) but both of these trees have teeth over the entire leaflet margin, tree of heaven only has a few teeth at the base of the leaflets.

Sources:

• FEIS - Ailanthus
• Invasive Plant Atlas: Tree of Heaven
• ASU - Ailanthus
• Northern Arizona Invasive Plants
• Harlow, William M, et al. Textbook of Dendrology. McGraw-Hill, 1979