Tree of Heaven Identification: Glands and Odor

Tree of heaven (Ailanthus altissima) is identified by the base of its leaflets. Penn State Extension describes one to two protruding bumps called glandular teeth at the base of each leaflet, with the rest of the leaflet margin smooth. Native trees that look similar from a distance — staghorn sumac, black walnut, hickory — have serrated leaflet edges all the way along, and that contrast is the key distinguishing feature.

The rest of the picture: a pinnately compound leaf that Penn State records at one to four feet long carrying ten to forty leaflets, a strong offensive smell when the foliage is crushed, smooth brownish-green young bark turning light brown to gray and resembling cantaloupe skin with age, and a large spongy brown pith visible wherever a twig snaps.

It grows fast and tall — Penn State gives heights up to 80 feet — which is why it turns up along fence lines, alleys, highway margins and any patch of ground nobody is watching.

Two reasons, both from Penn State Extension.

Spread. A female tree can produce more than 300,000 seeds annually, dispersed in one-to-two-inch twisted samaras, and root suckers may extend up to 50 feet from the parent tree. It also produces toxins that hold back competing plants, so it can take over roadsides, fields and natural areas and crowd out natives.

Spotted lanternfly. Penn State states that tree of heaven is a preferred host plant for the spotted lanternfly, an invasive insect first documented in Pennsylvania in 2014 that has been observed feeding on more than 70 species of plants and trees. Managing ailanthus has become a core part of lanternfly management, either by removing it or by keeping and systemically treating selected trees as trap trees.

If you have found tree of heaven and you are in or near a lanternfly quarantine area, report it to your state department of agriculture — several states run reporting tools for exactly this.

Penn State is explicit: simply removing the tree causes it to send up vigorous stump and root sprouts, so cutting alone makes the problem worse. To control tree of heaven you have to control the roots, and cutting the stem and painting the stump will not stop root suckering on its own.

What that means in practice:

• Plan control around the root system, not the trunk
• Expect suckers to appear well away from the stump — Penn State's figure is up to 50 feet
• Follow your state's herbicide label and timing guidance, or hire a licensed applicator
• Ask your county extension office for the current recommendation before you start, because timing matters and products change

Penn State also notes that a few cases of skin irritation or dermatitis have been reported from contact with plant parts, and rare cases of myocarditis from sap entering broken skin. Wear gloves and long sleeves when cutting, and wash up afterwards.

All four have long pinnately compound leaves, and in a hedgerow at forty feet they can look alike. Work through this order:

• Leaflet margin. Smooth along the edge with a bump or two at the base means ailanthus. Serrations running the length of the leaflet mean a native species, per Penn State.
• Smell. Crush a leaflet: tree of heaven gives off a strong, offensive odor.
• Twig. Snap one. Large, spongy, brown pith points to ailanthus.
• Bark. Mature ailanthus bark is light brown to gray and Penn State compares the pattern to the skin of a cantaloupe.
• Fruit. Twisted samaras one to two inches long, often in dense clusters on female trees.

Photograph a whole leaf flat, a close-up of one leaflet base, and the bark. Those three answer it — and they are the shots to take before you photograph it with the app and let it identify the tree.