Botany of American Sweetgum Trees
The subject of this article is American sweetgum trees, that is, what plant taxonomy classifies as Liquidambar styraciflua. While a specific type is recommended here, namely, Liquidambar styraciflua 'Rotundiloba,' all information is about the species plant, unless otherwise noted. Rotundiloba is a sterile, non-fruiting culitivar (that is, it does not produce the famous balls known as "gumballs" that serve as seed pods).
American sweetgum trees are deciduous trees, native to the southeastern United States. They belong to the Altingiaceae family.
Features of the Plant
American sweetgum can reach 80 feet in height at maturity, with a spread of about 60 feet. The leaves, which are five-lobed and shaped like stars, provide excellent fall foliage color. In some cases, at the peak of the fall foliage season, certain leaves may be red, others purple, others yellow, others orange (all on the same plant). On some trees, the branches are "winged," as on winged euonymus (burning bush), displaying corky flanges. The bark on the trunk is deeply furrowed.
Most people consider their seed pods (also called "fruits," "balls," "gumballs," "capsules") to be a negative, making it a landscaping mistake to grow these plants. The seed pods make them among the messiest of trees to grow. While they are, in fact, messy, they are hardly the nuisance that the fruits from a female Ginkgo biloba are. Not only are they messy for you, but they are also potentially messy for your neighbors. If you live uphill from a neighbor, the gumballs may roll downhill onto the neighbor's property when they drop.
That is why the fruitless Rotundiloba is the recommended cultivar to grow. Rotundiloba grows 60 to 70 feet tall; its spread, at its base, is about 30 feet (narrower the closer you get to the top). Even a Rotundiloba may eventually produce a gumball here or there, but such a stray seed pod will be treated as a novelty rather than as a nuisance. Rotundiloba can be grown in zones 5 to 9.
USDA Plant Hardiness Zones, Preferred Growing Conditions, and Care
American sweetgum trees are best grown in USDA plant hardiness zones 5 to 9. They are fairly drought-tolerant trees once mature. Grow them in full sun and in loamy soil that is on the acidic side. Fertilize them occasionally with compost.
When You Can't Find (or Don't Want) the "No-Gumballs" Variety
Although most find the spiky pods (which look like they belong on a medieval weapon) messy, they do have their uses. Craft enthusiasts use them decoratively in, for example:
- Christmas kissing balls
- Christmas wreaths
- Dried floral arrangements
Some gardeners report success using them as a "pest-control mulch" (critters such as wild rabbits do not like stepping on their spines). Wildlife (birds and rodents) eat the seeds.
But if you are not involved with crafts (and if you dislike unnecessary landscape maintenance) you probably will not be a fan of these gumballs. If you can't find the pod-less 'Rotundiloba,' but you still wish to grow American sweetgum trees, plant them in an area where you will not have to bother cleaning up the pods. For those with sufficient room on their properties, one option may be to incorporate the "messy" sweetgum trees into woodland gardens.
Outstanding Features of American Sweetgum Trees
American sweetgum trees are moderate-to-fast-growing trees. But their best feature has to be their fall foliage color, which is not only rich, but also varied. You will appreciate the fact that you can get more than one autumn color on the same tree, which is also true of some maple trees. Another good feature of this plant is that its fall foliage develops rather late in the autumn (November in zone 5), meaning that it gives your landscaping color after the leaves of the sugar maples and red maples (for example) have dropped off their branches.
Other Types of Sweetgum
Within the Liquidambar genus, there are more species than just styraciflua, as well as well as cultivars other than Rotundiloba. Horticulturist, Michael Dirr lists and describes several, as follows:
- L. formosana: a good choice for the South, since, when mature, it becomes even more drought-tolerant than most sweetgums do; zones 6 to 9, 40 to 60 feet tall and wide.
- L. acalycina 'Burgundy Flush': This cultivar starts out in spring with burgundy-purple-bronze leaves. It becomes about 50 feet tall and 25 feet wide. Grow it in zones 6 to 8.
- L. styraciflua 'Slender Silhouette': Even narrower than Burgundy Flush, this plant truly bears a columnar shape, standing about 50 feet tall at maturity, with a width of only about 4 feet. Grow this skinny tree in zones 5 to 8.
- L. styraciflua 'Variegata': This is just one of several variegated types that you can buy. Its otherwise green leaves are streaked here and there with yellow or off-white markings. Its maximum height is 60 feet, and its maximum spread is 25 feet. It is suited to zones 4 to 10.
- L. styraciflua 'Gumball': This is dwarf kind that takes on a shrub form. It reaches just 5 feet by 5 feet. It can be grown in zones 5 to 8.
Name Origins, Uses in Landscaping and Elsewhere
These trees do yield a type of gum called "liquid amber," thus accounting for both the genus name and the common name. According to the Illinois State Museum, "The sweetgum sap is also referred to as American styrax (hence the species name, styraciflua) and some use it as a chewing gum."
The Cornell University Extension observes that this gum has also been used medicinally to, among other things, "ease sore throats, coughs and colds." Meanwhile, "Rotundiloba" refers to the leaves' rounded lobes on the fruitless cultivar (think of the adjective, "rotund"). By contrast, the leaves on the species tree are pointed.