American Sweet Gum Tree: An Attractive Plant With Drawbacks
A Tree for Gardens and Landscaped Areas
The American sweet gum tree is an attractive plant that produces beautiful leaf colours in the fall. It's grown as an ornamental tree in southwestern British Columbia, where I live. It's an introduced plant in the province but does well here. I don't have a tree in my garden, but some lovely specimens are located close to my home. I'm able to observe them on a frequent basis.
The tree can be a great addition to either a garden or a landscaped area. The location for the tree needs to be considered carefully, however. The spiky fruits that it drops can sometimes cause problems. The plant has other interesting features besides its autumn leaf colour and its fruits. These features might include health benefits.
The scientific name of the American sweet gum (or sweetgum) tree is Liquidambar styraciflua. The genus name is derived from the phrase "liquid amber", although it's spelled differently. The name refers to the scented sap released when the trunk is damaged. The resinous sap is a thick and gummy liquid at first and is yellow to amber in colour. Some people use the semi-hardened sap as chewing gum. The word "sweet" in the tree's name refers to the scent of the gum, not the taste. The gum is said to taste slightly bitter.
The tree belongs to the family Altingiaceae and is native to the eastern part of the United States and Mexico. Until quite recently, it was placed in the witch hazel family, or the Hamamelidaceae. Studies of its genetics have shown that the genus Liquidambar should be classified in a separate group from witch hazel. The older family name is still used by some people, however.
The tree grows in USDA (United States Department of Agriculture) plant hardiness zones 5 to 9. It does well in southwestern BC. Our winters are mostly mild, unlike the case in the rest of the province. We sometimes get a little snow in winter, but it doesn't last for long (except on the mountain tops).
Trunk and Leaves
The tree is usually between sixty and eighty feet tall when it's mature and has a spread of around fifty feet. It occasionally reaches a height of a hundred feet or more. Multiple cultivars of the plant are available, so people can choose one that is likely to have the characteristics that they want, such as a suitable height. The bark of the trunk is grey and has irregular ridges and furrows. The wood is sometimes used to make furniture and veneer.
Sweet gum leaves resemble maple leaves but are more deeply divided. They have five narrow lobes and occasionally more. The leaves are star shaped. The edges of the lobes are finely serrated. The leaves are attached to a branch by a long petiole, or leaf stalk.
In the autumn, the leaves turn a beautiful shade of yellow, orange, pink, purple, and red. They are often multicoloured. Their appearance is a major reason for the popularity of the tree. The tree is disliked as well as loved, however, as I explain below.
Flowers, Fruits, and Seeds
The mature tree produces greenish-yellow flowers in the spring. The flowers are small, but they are grouped together to make larger structures. The plant is monoecious, which means that male and female flowers are present on the same tree.
Male and Female Flowers
The male flower-bearing structure is an upright spike that is two to three inches long. The female flowers are borne in a roughly spherical structure that often hangs from the plant via a stalk. The structures that bear the flowers are shown in the photo below. The flowers are pollinated by wind that carries pollen from a different sweet gum tree.
Fruits or Gum Balls
The female structure becomes a green and spiky ball as it matures. The structure is made from multiple flowers and therefore contains multiple fruits. It becomes brown as it ripens and is known as a gum ball. Gum balls growing close together may stick to each other, forming a chain or cluster.
An individual gum ball contains capsules that each bear several seeds. The seeds are released through an opening in the capsule. Though many of the mature gum balls fall to the ground after releasing their seeds, some stay on the trees during the winter.
Potential Problems Caused by Gum Balls
Walking barefoot under a sweet gum tree that has dropped its fruits can be a painful experience. The gum balls are sometimes so numerous that if they fall on a sidewalk they may be risky to walk on and cause problems such as sprained ankles. They can also be painful for dog paws. It's suggested that the tree is planted far away from a sidewalk for these reasons. Another potential problem that may develop near a sidewalk is that the tree's roots may damage the pavement.
I haven't read reports about serious problems caused by the gum balls where I live. Perhaps they exist but I've never encountered them, or perhaps the tree produces fewer fruits in my area and is less problematic than in warmer climates. I recently noticed than one of the two sweet gum trees growing by the school shown in the second photo in this article has been removed, however. This was presumably because of a problem with the tree or its effects.
The felled tree appeared healthy to me. I suspect that its removal was due to the fact that the tree was further away from the building and the playground than the tree in my photo and was creating supervision problems. On one occasion during school hours, I noticed children gathering gum balls from below the second tree (but not the first one nearer the school) and throwing them at each other.
As annoying as the gums balls may be, some people enjoy using them in crafts. An Internet search for "sweet gum ball crafts" should bring up some interesting ideas. The balls are used to make Christmas tree ornaments and are added to dried flower arrangements and other decorations, for example.
Clearing the balls from the ground can be difficult, even where I live. The video below shows a cultivated variety of the plant (Liquidambar styraciflua 'rotundiloba') that doesn't produce fruit.
Growing the Tree in a Garden
The local garden centre that I visit says that American sweet gum should be grown in full sunlight and in average to moist conditions. These recommendations are for southwestern British Columbia, where the tree probably needs as much sun as it can get, but U.S. websites agree with the recommendations.
The Missouri Botanical Garden says that the plant needs full sun and moderate moisture. A University of Kentucky web page also says that the plant likes moist soil. The plant doesn't do well in alkaline soil. It's reportedly resistant to deer and rabbits. The lifespan estimates that I've read say that the tree can live from eighty to a hundred and fifty years.
The trees are often bought as seedlings, but some people like to grow them from seeds. The potential height and spread of the tree should be kept in mind. It should be planted away from obstructions or objects that it might damage. One tree in my area has been planted beside a sidewalk at the start of a walking trail. The sidewalk is cracked in multiple places near the tree. This may be a coincidence, but cracked sidewalks are said to be a problem caused by the tree's roots.
The gum produced by the tree is known as American storax or simply as storax. The later term is also used for gum obtained from other plants. Claims of multiple health benefits for American storax exist. As the WebMD website says, there is insufficient evidence to support these claims at the moment.
The gum was used as a traditional medicine by the native people of the United States and by European settlers. I think that traditional medicines are worth investigating. Today the gum is used to give a pleasant fragrance to perfumes and soaps. It's also used as a fixative to prepare specimens for examination under a microscope.
The gum appears to be safe to chew in small amounts. although I don't know how the chewing action affects the teeth and any dental work. Moderate amounts may cause diarrhea or a rash. Large amounts may be dangerous, as the quote shown below indicates. Since the details of how the gum affects the body are unknown, pregnant and nursing women should avoid using it.
Do not take large amounts by mouth or apply large amounts to open wounds. This can cause serious side effects including kidney damage.— WebMD website (in reference to American storax)
Fighting Bacteria and Viruses
The gum contains chemicals that might fight some species of bacteria. More research is need to confirm the possibly beneficial effects of the gum. I hope this research is done soon. We need help to fight certain infections at the moment due to the development of antibiotic resistance in bacteria.
Sweet gum also contains shikimic acid. This is the starting chemical in the multi-step process used to make Tamiflu®, a drug that fights flu viruses. The drug is also known as oseltamivir. The presence of shikimic acid in sweet gum is interesting, but more research is needed in order to find out whether it's important. The concentration of the chemical in sweet gum is lower than that found in some other plants.
Some people list wonderful benefits of sweet gum sap as though they are proven facts. Perhaps one day they will be, but additional investigations and discoveries are needed in order to prove that the claimed health benefits of the plant are real.
If a chemical in the plant is proven to be helpful, researchers will need to determine the amount or concentration that is most beneficial for us while still being safe. The chemical may need to be extracted from the plant and then purified and concentrated in order to be both effective and safe. This process needs to be economically worthwhile. If another plant has a higher concentration of a useful chemical, it may be better to concentrate research efforts on that organism.
An Interesting Sight
I'm happy to see the tree growing near my home. I wouldn't grow one in my garden due to its potential size and the possible effects of the gum balls on my dogs' feet. Seeing the trees beside a managed trail in my neighbourhood and in nearby gardens is always interesting, however. I see the gum balls on the grass, sidewalks, and gutters in my neighbourhood, but not in huge amounts and only in certain locations.
I sympathize with people who live in areas where the tree is more common and the gum balls more numerous and more annoying. I think the tree is lovely, but I can understand why some of the comments that I read praise the plant and others express dislike for it. In my part of the world, the plant seems to be more praised than disliked. It's a pleasant sight in a garden or landscaped area. I always enjoy examining sweet gum trees during my walks.
- Sweet gum information from the Missouri Botanical Garden
- Facts about the sweet gum tree from the Encyclopaedia Britannica
- Economic botany and cultural history of sweet gum from the University of Kentucky
- Liquidambar styraciflua facts from the GardenWorks plant database
- American storax facts and precautions from WebMD
- Extracting shikimic acid from sweet gum (Abstract) from SpringerLInk
- Shikimic acid information from Chemistry World, Royal Society of Chemistry
© 2019 Linda Crampton