Sweetgum, Redgum, Liquidambar styraciflua

Sweetgum (Liquidambar styraciflua), or Redgum, is one of our more attractive native trees, and is widely used in landscaping. Its leaves turn scarlet and orange in the fall, and its prickly fruits add lots of interest in the winter. Notice that “Redgum” is also a common name for a variety of Australian Eucalyptus, but you won’t find them growing in Ohio.

The star-shaped leaves of Sweetgum are distinct. The leaves and branches are alternately-arranged, i.e., they are not attached directly across from one another. They are also simple, and do not share a stem with other leaflets in groups of 3, 5, 7, etc., as is the case with compound leaves. The leaves are somewhat like those of Sugar Maple (Acer saccharum) as they have palmately-arranged (hand-like) veins, rather than pinnately-arranged (feather-like) veins. The 3- to 6-inch leaves have 5 (rarely 7) lobes and distinct teeth. The deciduous leaves are dark green in the summer, and often show lovely orange and red colors in the fall. Sweetgum leaves typically have a distinct star shape, but some have smaller, secondary lobes. This variation is said to be randomly distributed, with no clear geographic correlation. Sweetgums have distinctive leaf scars and buds. The leaf scars are crescent-shaped, with three small, round bundle scars. The buds have clearly visible, overlapping scales.

Left to right: Alternative, Opposite, Pinnately veined, Palmately veined. Sweetgum leaves
are alternately arranged and palmately veined. Images by Mort Schmidt

Sweetgums are monoecious – they have male and female flowers on the same tree. The flowers have no petals or sepals. Male flowers consist of an upright, somewhat conical cluster of spheres. Female flowers are spherical and hang from a long stem. The flowers are wind-pollinated. The female flowers turn into hard, 1- to 1.25-inch spherical fruits with pointed spikes. The brown fruits are persistent and often remain on the tree until spring, when the next year’s crop of young, green fruits start to form, making Sweetgum recognizable any time of year. Trees start to produce seeds at an age of 20 to 30 years, and continue for more than 100 years. Sweetgums also reproduce through sprouting from roots and stumps.

Clockwise from upper left: Sweetgum summer leaves, fall leaves, bud and
leaf scars, flowers, and fruit. Photos by Mort Schmidt

Sweetgum bark is medium gray and deeply furrowed, but usually not especially distinct, at least to my eye. However, immature trees and limbs occasionally have distinct, corky ridges.

Left-Mature Sweetgum bark. Right-Juvenile Sweetgum bark showing corky ridges.
Notice also the secondary lobes on the leaves. Photos by Mort Schmidt

Mature Sweetgums typically have a height of 60 to 100 feet and a trunk diameter of approximately 1.5 to 3 feet. Ohio’s Champion Sweetgum, located in Athens County, has a height of 121 feet, a trunk diameter of 4.4 feet, and a crown width of 89 feet.

ID Summary: Star-shaped leaves and persistent spherical fruits with sharp spikes. Corky ridges sometimes on branches.

Similar Trees: Leaves palmately-veined like Sugar Maple or Sycamore (Planatus occidentalis), but narrower and more star-shaped. Sweetgum leaves are alternate, maples are opposite. Sweetgum fruits similar in size and shape to Sycamore, but harder and spiked.

Clockwise from top left: Sweetgum leaf, Sugar Maple leaf, Sycamore leaf,
Sweetgum fruit, Sycamore fruit. Photos by Mort Schmidt

Liquidambar styraciflua is often found in bottomlands, and prefers moist, but not flooded soils. It tolerates poor soil, and thrives in clay-rich, somewhat acidic soils. Sweetgum does poorly in alkaline and sandy soil, especially in shady environments. As might be expected of water-tolerant trees, Sweetgums are fire-intolerant. Why evolve fire-resistance in environments unlikely to see fire? However, they’re well equipped to survive strong winds. Small twigs are weakly attached, and break off in major storms, leaving the trunk and larger branches intact.

Sweetgum grows in association with Tuliptree, Pin Oak, and Northern Red Oak, but is sometimes found in pure stands.

Sweetgum is native to the southeastern U.S., including southern Ohio, Mexico, and Central America, but in Central Ohio, it’s mostly seen in landscaping. Lucy Braun’s The Woody Plants of Ohio shows Sweetgum in 13 of Ohio’s southern counties. The Columbus, Ohio Street Tree Inventory indicates that Sweetgum is the 28th most common tree on Columbus streets, making up 0.92 percent of the total.

Sweetgum range map. Image from USDA Forestry Service

Sweetgum lumber has a Janka hardness of 850 lbf and a density of 0.55 g/cc, according to the Wood Database, compared to the median of my list of 73 Ohio trees of 1,075 lbf and 0.64 g/cc, and on par with Black Cherry (Prunus serotina). Sweetgum is fine-grained, smooth, with dark heartwood, sometimes called, “satin walnut”. Unfortunately, the lighter sapwood surrounding it is thick, so only larger logs provide a significant quantity of heartwood. The wood has cross grain, making it split-resistant, but it lacks dimensional stability. Like most dark woods, the heartwood is fairly rot-resistant, but it’s not particularly insect-resistant. Sweetgum works well and takes glue, stain, and paint. Gum was more popular in the early 1900s, but the lumber is still used in making interior trim, furniture, and turned objects. Sweetgum wood products include veneer, plywood, flake board, and pulp for high-grade papers.

According to the Native American Ethnobotany Database, the Natives used Liquidambar styraciflua in a number of ways.

Cherokee:

Inner bark or rosin for diarrhea and dysentery,
Gum used on wounds and mixed with tallow to stop itching,
Gynecological use of bark to reduce bleeding,
Gum used as a drawing salve,
Gum used for chewing,

Houma:

Decoction of roots applied to skin for sores caused by worms,
Decoction from Spanish moss growing on Sweetgums for treating fevers,

Koasati:

Decoction of bark for “night sickness”,

Rappahannock:

Decoction from dried bark to treat dysentery,
Hardened sap placed in dogs’ noses to treat distemper.

Liquidambar resin can be extracted by boiling and pressing the bark. The resin, also known as “storax”, is a semi-solid material with an aromatic odor, and is, or was used as chewing gum, medicine, and as an additive for perfume and soap. (Traditional chewing gum was made of chicle from the Sopadilla tree, not the Sweetgum, and is now made from synthesized gums). Asian varieties of Liquidambar were used to treat diarrhea, coughs, skin conditions, dysentery, and rheumatism. Storax production is generally best in Asian varieties of Liquidambar, and from L. styraciflua grown in its southern range. The aromatic extracts from Sweetgum are similar to those of the Australian Tea Tree, known for its antimicrobial properties.

Sweetgum was formerly placed in the Hamamelidaceae family, together with Witch Hazel, and their extracts have similar astringent uses. However, Sweetgum has been reclassified as a member of the Altingiaceae family, on the basis of molecular studies. This reminds us that biological classification is a human endeavor, and the schemes are not set in stone. Contrary to common belief, science is not about certainty – it’s about consensus. If the majority of experts in a field agree on something, it’s regarded as fact, with the understanding that new data could require us to revise our interpretations.

Storax derived from plants of the genus Liquidambar, and the genus Styrax, is used as a fixative in perfumes, and is added to soaps, cosmetics, incense, and as a flavoring in tobacco. Sweetgum resin was also formerly used as an adhesive and lacquer. According to HellenicGods.org, storax is one of the ingredients used by the ancient Egyptians for mummification.

The aromatic properties of Liquidambar sap might have evolved to serve as an insecticide, because relatively few insects feed on Sweetgum. The luna moth and large paectes moth feed on Sweetgum leaves, while mourning doves, eastern towhees, Carolina chickadees, purple finches, and white-throated sparrows eat the seeds. Seeds also are a minor source of food for gray squirrels and eastern chipmunks.

S. Theresa Dietz’s The Complete Language of Trees indicates that wearing or carrying a Sweetgum seed pod will protect the wearer from evil. A bowl with Sweetgum pods will similarly protect one’s house. Unpleasant odors were once thought to be a source of illness, various sources, including Liquidambar was used to purify the air and ward off plagues. Gloves treated with Liquidambar were held in front of the face with the belief that they protected the wearer from disease.

Sweetgums are beautiful trees, and typically very hardy. They’re a good choice for planting in urban settings if you can live with the spiny fruits.