Tree of Heaven: Recognizing and reporting this invasive tree

August is tree check month, and there’s no better time to spotlight one of Ontario’s most notorious invaders — the tree of heaven. Once an introduced ornamental, this fast-growing species now thrives in the most unexpected places: sprouting from sidewalks and the sides of buildings, lining our railways, and setting the stage for the arrival of another invasive threat — the spotted lanternfly. Chances are, you’ve seen this tree before without even knowing it. So, what makes it so problematic, how can you identify it, and what should you do if you find one? Read on to uncover the answers and help protect Ontario’s landscapes.

Recognize me? The tree of heaven grows all across southern Ontario along our roadways and in our neighbourhoods!

Article Authored by Raylene Colautti and Cassie Russell

What is Tree of Heaven?

The tree of heaven (Ailanthus altissima) is an invasive species in Canada that originates from China and Taiwan. In 1784, the first tree of heaven (TOH) was brought to North America from China to the USA as an ornamental. The tree of heaven’s ability to tolerate a wide variety of soil conditions, as well as its exceptional drought and pollution tolerance, made it a desirable tree species in urban environments.

While TOH cannot be sold or propagated in Canada, that has not stopped this tree from spreading on it’s own accord. TOH can reproduce both sexually (through seeds produced by female trees) and asexually (via vegetative growth from root suckers). It responds aggressively to pruning by producing vigorous regrowth in the form of suckers and is often found in groves consisting of numerous smaller trees.

Due to its resilience and ability to rapidly grow and reproduce, TOH quickly spread and established itself across British Columbia, Quebec, and Ontario. Today, the tree of heaven can be found in a variety of landscapes from forests to the sides of roads to even growing between cracks in the sidewalk or out of building foundations!

How to identify it

To an untrained eye, the tree of heaven may fail to stand out, but there are many distinguishing features that separate this invasive tree from the rest!

LEAVES: The tree of heaven has large and pinnately compound leaves, meaning each leaf is composed of multiple smaller leaflets. The leaflets can be alternately OR oppositely arranged around a central stem and at the end of the stem a single terminal leaflet will grow. The leaflets have smooth margins and “glandular teeth” at the base of each leaflet – circled in the photo below. The number of leaflets on a stem can range from 10 to 41 pairs and the leaves can range from 30 to 120 cm in length. Another identifying trait is that the leaves and other plant parts may smell distinctly of rancid peanut butter, especially when crushed.

BARK: The bark of the tree of heaven is noticeably smooth. It is brownish-green when young and turns light grey and develops fissures as it matures. Along the twigs, large heart-shaped leaf scars are present.

TOH bark on older trees is slighty more textured but still smooth and light grey in colour

SEEDS: At this time of year, you may notice colourful clusters that resemble keys on some trees. These are called samaras, which are produced by female TOH and help the tree stand out amongst other trees with compound leaves. Samaras are winged dry ‘fruits’ that are 2-5 cm in length. They contain a single seed and serve as the tree of heaven’s main method of reproduction. The tree of heaven’s samaras distinctly stand out amongst the foliage and other trees due to their redish-pink and green colouring that appear when the fruits are preparing to drop. It’s important to note that TOH is dioecious, meaning individual trees are either male or female. Only female trees will produce these distinct fruits.

Bright red-pink samaras on a TOH are easily seen from mid July through August in Ontario. Photo: Chuck Bargeron, University of Georgia, Bugwood.org

The tree of heaven can also spread via the production of suckers which grow from the roots of the main tree. This kind of spread can lead to groves of TOH appearing at a single location, densely compacted together.

Multiple TOH growing close to one another in a grove

Where you might find it

The tree of heaven can grow in just about any spot that’s sunny and warm enough to allow it to thrive. Before it was classified as an invasive species, TOH was purposely planted, which means large mature trees can be found in old parks, green spaces or even on residential properties. More commonly, tree of heaven has invaded disturbed areas where other trees can’t always thrive, such as along railways, the sides of roads and highways, or abandoned spaces.

Due to their resilience for tolerating less than ideal conditions, they can also be found growing out of the sides of houses or through cracks in the concrete. In older areas of Toronto and Hamilton especially, it’s not hard to find TOH taking up real estate in alleys between old buildings.

Tree-of-heaven growing along Interstate Highway in the US. Photo: Chuck Bargeron, University of Georgia, Bugwood.org

Mature TOH growing beside a walking path close to Queen Street West in Toronto, ON. This tree would have been purposely planted decades ago, before TOH was deemed invasive. Just one of the many examples of these trees growing close to rail lines and major highways like the Gardiner Expressway, pictured on the left.

Confusing look-a-likes

The trees most commonly mistaken for tree of heaven are sumac species (Rhus sp.) and black walnut (Juglans nigra).

The tree of heaven and sumac are quite similar: both have compound leaves and smooth bark and can be found in similar environments; however there are some key differences. It is easy to differentiate between the two species at this time of year, as sumacs are producing bright red fruit clusters which are clearly distinguishable from the samaras produced by the tree of heaven. Upon closer inspection, more differences between the species are noticeable. The leaflets on sumacs have toothed margins, whereas the leaflets of trees of heaven have those smooth margins with one or two glandular teeth mentioned earlier. Additionally, young sumac branches may be hairy, whereas the young bark of the tree of heaven is never hairy.

Sumac leaves are pinnately compound and leaflets have serrated edges. (Source: John Cardina, The Ohio State University, Bugwood.org)

The black walnut tree may also be mistaken for a tree of heaven, due to its similar pinnately compound leaves. A noticeable difference between the leaves of the two species is the black walnut leaflets have finely serrated leaf margins, whereas the tree of heaven leaflets have smooth leaf margins. The bark of the two species is also distinctly different, with the black walnut having a coarser bark texture with deep furrows compared to the smooth bark of TOH. And of course, the black walnut produces large spherical nuts encased in a fleshy green hull as a method of reproduction and does not produce samaras like the tree of heaven does. The nuts are easily visible this time of year, making for a quick and easy ID.

Black walnut bark is coarse with deep grooves, and its leaflets have serrated edges. (Source: Jason Sharman, Vitalitree, Bugwood.org)

Where to report TOH and why you should do it!

So you think you’ve found a tree of heaven: What now? Although the tree of heaven is widespread across Ontario, it is still highly important to track the spread of this invasive species to better understand its distribution in Ontario. While some individuals may opt to remove these trees, the suckering nature makes them a very challenging tree to fully get rid of without the use of herbicides.

Now more than ever, it is important to record observations of tree of heaven as it is one of the preferred hosts of the spotted lanternfly (SLF), an invasive species not yet established in Canada, but one which we are monitoring closely for. Reporting tree of heaven locations can help those who are monitoring for SLF to identify potential surveillance sites, so if any SLF populations arise in the future we have a better chance of detecting them early on.

If you see a tree of heaven in your area, you can report your sighting to EDDMapS (https://www.eddmaps.org/) or iNaturalist (https://www.inaturalist.org/).

Currently, there are just over 1200 potential observations of Tree of Heaven in Ontario on iNaturalist as of August 2025. Note some of these observations have not been verified and may not represent the actual distribution of TOH in Ontario.

TOH and Spotted Lanternfly

Although the tree of heaven is not an obligate host for the spotted lanternfly (ie, it doesn’t require it to complete it’s lifecycle), it is a highly preferred host, making it a great surveillance tool as we try to monitor for SLF’s arrival in Canada. Therefore, by knowing the locations of these trees across Ontario we can better hone in our surveillance and more strategically plan out the location of traps. SLF has the capacity to cause serious damage to Ontario’s grape & wine industry, while also feeding and weakening over 100 different plant hosts grown in the nursery and landscape and can quickly grow into a nuisance for the public. We need everybody’s help to monitor for this pest, and a great place to start is by reporting and monitoring their favourite tree of heaven!

Spotted lanternflies gathering on the trunk of a tree of heaven, one of their most preferred hosts. (Source: Richard Gardner, Bugwood.org)

Additional Resources

Care to share the word? There’s lots of great webpages and fact sheets out there to share among your networks:

Tree-of-Heaven | Ontario’s Invading Species Awareness Program

Identifying Tree-of-Heaven

Tree of Heaven – BC Resource Sheet

Tree of Heaven – Invasive Species Centre

Eastern Black Walnut vs Tree of Heaven: Identification – bplant.org

Tree of Heaven vs Staghorn Sumac: Identification – bplant.org