How do I identify Tree of Heaven?

Tree of Heaven (Ailanthus altissima) has large compound leaves with many narrow leaflets, each with a small notch near its base. Crushed leaves have a strong, unpleasant smell. The bark on young trees is pale grey with shallow vertical striations. It is very common in disturbed urban areas.

How do I tell Norway maple from sugar maple?

Break a petiole (leaf stem): Norway maple exudes milky white sap; sugar maple's is clear. Norway maple leaves also have sharper-tipped lobes and its seed wings spread at nearly 180 degrees, much wider than sugar maple.

Are invasive trees dangerous to people?

Most invasive trees are not directly dangerous to people, but some cause skin irritation on contact with sap and others produce berries that should not be eaten. Never eat any part of a plant or tree based on an app identification alone.

Canopy · Identification

Common Invasive Trees in North America: How to Identify Them

Guide · 3 min read

Not every tree growing in a North American park or woodland belongs there. Several widespread species are invasive from other continents, grow aggressively and outcompete native vegetation. Being able to recognise them is the first step in understanding their impact.

Quick answer: Common invasive trees in North America include Tree of Heaven, Norway maple, Siberian elm and white mulberry. They can often be identified by distinctive leaf shape, bark texture or seed structure. Never eat any part of a plant or tree based solely on an app identification.

Tree of Heaven (Ailanthus altissima)

Origin: China.
Leaves: compound and pinnate, with 11 to 41 leaflets; each leaflet has a small notch and gland near its base.
Bark: pale grey with shallow vertical striations resembling a cantaloupe's skin on young trees.
Smell: crushed leaves have a strong, acrid, unpleasant odour. This is a reliable field mark.
Where found: disturbed urban areas, roadsides, vacant lots; extremely drought-tolerant.

Norway maple (Acer platanoides)

Origin: Europe.
Leaves: similar to sugar maple, but the lobe tips are sharper; breaking a petiole releases milky white sap (sugar maple's sap is clear).
Seeds: samaras have wings at nearly 180 degrees, much wider than sugar maple.
Where found: urban parks, roadsides and forest edges across the eastern and northern US.
Impact: forms dense shade that suppresses native understory plants.

Siberian elm (Ulmus pumila)

Origin: Asia.
Leaves: small, narrow, with a symmetric leaf base; native elms have asymmetric bases.
Bark: rough and grey with deep furrows; branches are brittle.
Seeds: flat and papery, produced in large quantities in spring.
Where found: Great Plains, Midwest and dry regions where it tolerates drought and cold.

White mulberry (Morus alba)

Origin: China.
Leaves: variable in shape, often lobed on the same tree; smooth on top, slightly rough below.
Bark: orange-brown with a fibrous, stringy texture.
Fruit: white to pinkish berry-like clusters in summer. Never eat tree fruit based on an app identification.
Where found: disturbed ground, roadsides and urban edges across most of North America.

Why identifying invasive trees matters

Invasive trees spread quickly and displace the native species that local wildlife depends on. Early identification helps land managers, gardeners and conservation volunteers respond before a single tree becomes a stand. Many invasive trees are controlled or removed in some states but spread freely in others; local guidance varies.

Canopy identifies trees from a photo of a leaf, bark, flower or whole tree, then opens a full species profile including native range, safety notes and seasonality. A species marked as introduced or naturalised in the profile is a signal to check whether it is considered invasive in your region. For a general introduction to leaf-based identification, see our guide to identifying a tree by its leaves.

Common questions

How do I identify Tree of Heaven?: Tree of Heaven (Ailanthus altissima) has large compound leaves with many narrow leaflets, each with a small notch near its base. Crushed leaves have a strong, unpleasant smell. The bark on young trees is pale grey with shallow vertical striations. It is very common in disturbed urban areas.
How do I tell Norway maple from sugar maple?: Break a petiole (leaf stem): Norway maple exudes milky white sap; sugar maple's is clear. Norway maple leaves also have sharper-tipped lobes and its seed wings spread at nearly 180 degrees, much wider than sugar maple.
Are invasive trees dangerous to people?: Most invasive trees are not directly dangerous to people, but some cause skin irritation on contact with sap and others produce berries that should not be eaten. Never eat any part of a plant or tree based on an app identification alone.

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