The largest tree beyond my door, and one of the largest trees in the immediate neighborhood, is a sweetgum. It probably isn’t that old and there are larger trees around, but it is still about 2′ in diameter and roughly 90 to 100′ tall, with furrowed light gray bark dappled with patches of a white crustose lichen on its trunk and pale green lichen on its branches (not as luxuriantly lichen covered as nearby oaks). Young sweetgums growing in a field have a conical, Christmas tree shape, and sweetgums actually have several ties to Christmas (this article was originally written for December). A sweetgum’s canopy usually becomes rounded with age, as is the case with this tree, and lower limbs growing into utility lines have been cut occasionally, so most of its great boughs are high in the air. It is a very exuberant tree. Many years ago it was surrounded by a grove of small sweetgums, at least some suckers from large exposed roots, and more still sprout. Some of the limbs of the big sweetgum develop vertical shoots that look just like large saplings several feet tall, later bending outward. Sweetgums probably aren’t meant to have a spreading form, and this tree has long had open space on most sides. Large sweetgums often have limbs that angle upward a short distance, with limbs closer to vertical branching off from the ends, and I might have seen how this form comes about. One calm summer evening a few years ago I was standing by a window when there was a whooshing sound and a huge, leafy limb fell, almost on our residential powerline. The top has been snapped off by lightning or wind at least once. Recently large pieces of a partially dead limb have fallen and there might be more dead branches than usual after the prolonged drought last summer and fall. At one time there was a very large squirrel nest made of leafy twigs in the principal fork high in the canopy, and hawk pairs have seemed to consider nesting in late winter. Birds often perch at the very top and during the winter some pry seeds out of the prickly ‘gumballs.’ Virginia creeper climbs up the wide trunk. Sweetgums might seem commonplace, but they have ecological and historical depths now largely forgotten.
Sweetgums are probably very familiar. In many places they are one of the first and most abundant woody pioneers to sprout in abandoned fields, joining other early successional trees like loblolly pines, cedars, winged elms, and ashes. Sweetgums bear large star-shaped leaves with five (sometimes seven or three) sharp, triangular points with slightly serrated edges, on very long petioles (leaf stems), and are often clustered on short side twigs. Along the west wall of UNC’s Coker Arboretum there is an unusual specimen whose leaves have five rounded points, an example of the Rotundiloba or roundleaf cultivar, apparently discovered in North Carolina in the 30’s and sterile. This tree is the state’s largest roundleaf sweetgum (90′ tall), according to the NC Forest Service, and there are others in the Arboretum. When bruised a sweetgum’s relatively thick leaves give off a characteristic, resinous fragrance reminiscent of pines. The leaves alternate along relatively thick twigs, green to bronze when young, spotted with pale lenticels, pores that allow the woody tissues to breathe, and sometimes corky growths. These warty growths can grow into “wings,” like those along the more delicate twigs of winged elms, which also grow in open areas and young woods, but sweetgums usually have smaller wings, if any, and have more robust twigs and buds than elms. Sweetgum twigs are supposed to have star-shaped pith in cross section, but I haven’t seen this so far. The furrowed but relatively soft pale gray bark, up to an inch or more thick, is one reason for the rare common name alligatorwood. The big sweetgum has light gray bark, very light gray on the south side (I wondered if the color was due to lichen, but it looks like bare bark), while a smaller sweetgum nearby has darker grayish bark.
The big, glossy greenish to bronze-colored terminal buds and smaller lateral buds, covered in a few large hair-fringed scales, glint in the wane winter sun, and it is a sign of spring when they begin to swell outside my window. It feels like no sooner do these big buds open, leaving pale yellowish bud scales littering the ground, then the spent male flowers also drop. Each monoecious tree produces flowers of both sexes, the yellowish green clusters of male flowers form spheres on stalks about 1 ½” tall, held upright at the twig tips as the shiny, vaguely spidery new leaves begin to unfold, while the female flower clusters hang as spiky green balls, much smaller than the mature fruit, each flower producing up to two seeds. The two styles of each flower become long spikes or beaks on the gumballs.
The dark brown mature ‘spiny’ gumballs can be seen dangling high in the air against the bracing skies of winter. They could be confused with the light brown balls of windborne seeds hanging on American sycamores, but sycamores have unmistakable pale bark, brown and flaking low on the trunk, becoming dappled green and then stark white at the treetops. In early winter I hear bits of pale grit falling on the leaf litter, and I think this come from the sweetgum, but their seeds are actually dark and resemble tiny miniature ash keys. Gumballs carpet the ground and a neighboring driveway by late winter, and help develop calluses when walked on bare foot the rest of the year, though they eventually wear down to merely rough balls.
In the fall sweetgums are valued for color, with leaves turning light yellow, red, and purple, sometimes nearly black.
As pioneers, sweetgums dislike shade and put on height quickly to keep their place in the sun. They can grow up to 150′ tall and 5′ across or more. The NC Forest Service lists two champion American sweetgums, a 134′ tall tree at Merchants Millpond State Park and a tree 138′ tall, but with the same circumference, in Wilson County. There are two national champion sweetgums, in Virginia and Texas. Two large sweetgums near the corner of Lawson and Lincoln streets at NCCU might be the largest I have seen by some inches, and pretty large sweetgums are common in the bottomlands along Northeast Creek. Reportedly a sweetgum can live for 400 years.
Sweetgum has been known as liquidamber, bilsted, red gum, star gum, and American storax. Its scientific name is Liquidambar styraciflua, coined by Linnaeus in 1753; the generic name meaning “liquid amber” while the specific name means “flowing with styrax (storax).” Earlier, in 1686, English naturalist John Ray had termed it Styrax liquida. Depending on the system, sweetgums are in their own family or are classified with witch hazels, uncommon woodland shrubs that bloom in winter on steep hillsides above Northeast Creek and elsewhere in the Triangle.
Sweetgums of some kind have been around for at least 99 million years and once grew across the Northern Hemisphere, but today there are only three other species: L. orientalis in Turkey and two species in East Asia, L. formosana and L. acalycina. American sweetgums range from southwest Connecticut through much of Eastern North America, south to Nicaragua. According to the Tropicos floral database, sweetgums are known as tzo-te in Chiapas and Guatemala, quiramba in Guatemala, and liquidambar in Belize, Honduras, and Nicaragua.
The Spanish recognized sweetgum by its fragrance when they first encountered it in the New World. The Old World’s storax or styrax, a fragrant resin, was used in incense, perfumes, medicines, added to wine, and applied to hair but the source was mysterious in Europe, beyond vendors in places like Constantinople. Linnaeus gave the name Styrax to a genus of small trees, some found here, thinking that one of them was the source, but today classical storax (or rosemalles) is thought to come from Turkish sweetgums, originally harvested by Turkey’s Yuruks, a nomadic Turkic group. This traditional industry is reportedly endangered. Apparently the Turkish sweetgum was scientifically described only in the mid-19th century. In his first hand account of the 16th century conquest of Mexico conquistador Bernal Díaz del Castillo describes the feasts presented to Aztec emperor Motecuhzoma Xocoyotzin. Included were “three tubes much painted and gilded, which held liquidambar [apparently called xochiocotzoquahuitl in native Nahuatl, referring to the pinelike fragrance] mixed with certain herbs which they call tobaco.” After eating the emperor would inhale a little smoke and sleep, a reported effect of storax. The Spanish might have first encountered American storax used in incense a few years earlier further down the coast of Central America. Several years after the war in Mexico, Álvar Núñez Cabeza de Vaca encountered sweetgums growing near Appalachicola in Florida during the Narváez expedition.
American storax, also called copalm balm, was described as a heal all by 16th century Spanish herbalist Francisco Hernández de Toledo, who spent several years researching in Mexico and Central America. John Banister is credited with introducing sweetgums to Europe in 1681. In 1839 styrene was first distilled from storax, and about a century later styrofoam was made from polystyrene. Storax was used to treat illnesses such as dysentery during the Civil War. An American storax industry developed during WWI, but was subsequently abandoned in favor of cheaper storax from abroad, only to be reactivated around WWII when the supply from the Japanese-held Taiwan was cut off. Apparently the expertise was only retained in Clarke County in southwest Alabama, making it the center of the wartime industry. A sweetgum there produces only ½ to one pound per year, and the amount is supposed to depend on the amount of foliage and increases going south.
In recent times storax has been used in salves, adhesives, fragrance, perfuming powders, perfume fixative, soap, and tobacco flavoring. It has been smoked for sleep, chewed for sore throat, colds, diarrhea, ringworm, catarrah, and applied to sores, wounds, piles, etc. It was used to clear mucous, and as an anti-septic and anti-inflammatory. Sweetgum leaf essential oil is chemically similar to Australian tea tree oil. The inner bark was boiled with milk to alleviate diarrhea. The resin has long been a chewing gum and teeth cleaner. Storax (not necessarily American) is supposed to be a component of commercially available compound tincture of benzoin.
Sweetgumballs are or were painted and hung on Christmas trees. They could probably also be used in crafting and if nothing else cats chase them. Chinese sweetgum balls, apparently called lu lu tong in Mandarin and softer than our gumballs, are used herbally.
Sweetgums are a prominent source of lumber, with heavy and strong but not very flexible wood. After about 60 years trees develop reddish heartwood below the white sapwood. Sometimes the sapwood was sold as sap gum and the heartwood as red gum. Unesteemed “gum wood” was often called satin walnut or hazelwood and could even be passed off as exotic Circassian walnut, rosewood, and mahogany. The wood polishes and stains well and the heartwood can display interesting figures. Sweetgum has been used in furniture, indoor trim, veneer, flooring, crates, cigar boxes, toys. barrels, boats, chopsticks, woodenware, plywood, railroad ties, and for pulp.
Many bird species, squirrels, and chipmunks feed on sweetgum seeds, while beavers eat the bark. Larvae of a sweetgum bark beetle bore in living and dead wood. Many moths eat the leaves as caterpillars, including several common geometers (inchworms), luna moths, promothea or spicebush silkmoths, hickory horned devils (the impressive caterpillars of regal walnut moths), imperial moths, sweetgum leafrollers, and the large Paectes. The big, ethereal light green to yellowish, long tailed luna moth, once known as the pale empress of the night, is relatively common and its caterpillars can feed on several tree species, but their abundance seems to vary greatly across the Triangle. They seem to be abundant around Falls Lake; a few years ago I would often notice the large black barrellike droppings of caterpillars under sweetgums and look up to see the thick green accordion-shaped caterpillars with yellow markings hidden high overhead. Luna moths might also be common around NCSU. On the other hand I’ve seen few around Jordan Lake or in Chapel Hill and Durham, though sweetgums are common there too (but tuliptrees might be the more common deciduous pioneer in Chapel Hill).