SWEETGUM
Liquidambar styraciflua
IMPORTANCE: A popular street tree coast-to-coast, noted for unique star-shaped leaves, outstanding fall colors, and spiny “gumball” seed fruits. (Also for decorative wood and medicinal resin.)
FAMILY: Hamamelidaceae (Witch-hazel). GENUS: Liquidambar (sweetgum).
COMMON URBAN SPECIES: 
Sweetgum (Liquidambar styraciflua) or American sweetgum, star-leafed gum, red-gum, gumtree, alligator-wood, blisted, sapgum.
CLOSE RELATIVES: Formosan sweetgum (L. formosana) or Chinese s. Oriental sweetgum (L. orientalis) or Turkish s.
TYPICAL CITY LOCATION: Streets, parks, parking lots, yards. Larger specimens: Watery recreation areas, campuses.
KEY FEATURES: Leaf is star-shaped, usually 5 points (lobes) but often 7; about 4–7″ across; long slender leafstalk; fragrant when crushed; texture smooth, lustrous, hefty; edges dully sawtoothed; color bright green in summer with outstanding range of rich fall colors. Leaves are alternate (not opposite) on twigs and drop late in autumn or in early winter.
Distinctive woody, spiny fruit, 1–1½″ wide. An aggregation of beaky, seed-containing capsules. Droops all winter from a spindly stalk and looks like a large brown burr.
Twigs and small branches may have conspicuous corky flanges or “wings,” but not always. Bark medium gray and roughly furrowed (smooth on many West Coast specimens).
Young trees take on reliable, narrowly conical shape, sometimes plump at bottom; in later years, upper crown spreads quickly to form irregular roundish or paddlelike shape. (Lofty forest trees are bare one-half to two-thirds up the trunk.)
AVERAGE MATURE SIZE IN CITY: 35–60′ high, 20–40′ wide, 1½–3½′ thick.
RECENT CHAMPION: 136′ height, 66′ spread, 23′ circumf., Craven County, N.C.
A STELLAR PERFORMER
They say that the American sweetgum is overplanted in some towns, even in the warm coastal areas where landscapers have their pick of dreamy species. But the virtues of this native tree make it very hard—and sometimes pointless—to resist.
Its foliage alone earns it a place in the pantheon of street trees. Not only does the sweetgum leaf form a symbolic star, but a big shining star, a star that keeps its heft and luster for up to three seasons, and a star that explodes with autumn hues even in mild temperatures. How many other trees bring the colors of an eastern October to the California coast? Very few.
Woody, beaky sweetgum fruit and star-shaped leaf with its long stalk.
The sweetgum leaf may be less than geometrically correct as a star—sometimes its small bottom “legs” sprawl sideways and its “arms” are more pudgy than angular—but it strives to be interdenominational. Though its most common form is as a five-pointed (lobed) star or pentagram, the arrangement of these points suggests the six-pointed Star of David. Often, two additional base lobes appear, as if equipping the star for new-millennium duty.
The virtues of the leaf go on. Its edges are ornamented with a serrated pattern. It rarely succumbs to damaging pests and disfiguring diseases, as do so many deciduous (falling) leaves. It emits a camphory fragrance when crushed, a hint of its contribution to the tree’s celebrated sap or “copalm balm” (see sidebar). In autumn it comes up with brilliant designer colors. Depending on tree variety and local conditions, leaves turn shades of yellow, ochre, orange, burgundy, scarlet, crimson, purple, blue, and brown. The color pageant may be less spectacular than that of the sugar maple’s, since not all leaves turn at once or with the same intensity. But sweetgum coloration can dazzle into early winter, when the maples are bare.
“It relieves wind in the stomach and dissipates tumors beyond belief,” reported the sixteenth-century herbalist Francisco Hernandez. “Added to tobacco, it strengthens the head, belly, and heart…”
What supposedly performed such miracles? It was the resin extracted from Mexico’s sweetgum tree, a tree the Aztecs called xochiocotzoquahuitl and which Europe would name Liquidambar (liquid amber) styraciflua (flowing with storax or aromatic resin).
As a guest of the Aztec emperor Montezuma, Hernando Cortés puffed a smoke of tobacco infused with the resin. Perhaps this gave him the “belly and heart” to subjugate his host.
The sweetgum of Mexico (and North America) does not actually flow with the resin known as storax, a time-honored perfumy balm from Turkey’s oriental sweetgum. But it does produce a similar resin known as styrax or copalm balm, which has often substituted in commerce for the oriental balm.
When the sweetgum’s bark is cut, it exudes a yellowish gum used in the manufacture of syrups and ointments. Though Hernandez may have overstated its medicinal properties, it long served as a folk treatment for skin irritations and wounds. At one point, Alabama was producing a pound of resin per tree in its styrax industry.
According to country lore, a flavorful chaw of gum could come directly from a bark wound. But lately, when nature writer Janet Lembke coaxed some gum out of a tree, she reported that it smelled like cinnamon, tasted like cardboard, and stuck to her teeth through two brushings.
TOP CREDENTIALS
More than just a pretty face, American sweetgum comes to town with a sterling résumé. Its natural range is impressive: a swath of eastern America, from Connecticut south to Florida and west to Missouri; and another strip from Texas through Mexico into Central America. It is a tough tree, one of only three surviving species (along with Chinese and Turkish sweetgums) from an ancient genus of some 23. It is a vigorous tree, growing up to 165 feet high and 5 feet thick in its forest habitats. In cultivation, it can flourish so abundantly that in 1997, one Florida nursery rushed to give away some 4,000 young sweetgums that were starting to shade its other, slower-growing stock.
Easy to establish as urban plantings, saplings grow from 12 to about 30 feet in as few as six years, given plenty of sun, moisture, and ample root space. Reliably, they take a neat conical form until middle age pushes the upper crown into the broad, irregular spread of a big shade tree. Established trees handle most soils, poor drainage, and the usual urban stresses and deprivations while still warding off natural invaders.
Already prized for its resin and lumber, the sweetgum was cultivated in about 1680 and soon made its way into European parks and gardens as an ornamental. One of its early appearances in U.S. cities was in the form of paving blocks hewn from the tree’s heavy wood. It did not distinguish itself as a road surface, but by the twentieth century, its foliage was lighting up American parks and streets.
Frederick Law Olmsted included it in his first plantings for New York’s Central Park. Cincinnati, Louisville, and other cities along the Ohio River pioneered in sweetgum plantings, which spread through the Midwest. Back east, Philadelphia planted it in proud rows along Independence Mall. Southeastern towns, where sweetgum already squatted along roadsides and cleared areas, could hardly avoid planting it. In Texas and Arkansas, its fall color was a blessed sight.
Western cities have swelled the sweetgum’s urban empire. Five percent of the public trees in tree-rich Sacramento, for example, are sweetgums. Each fall in such cities as Los Angeles and San Francisco, sweetgums blaze on downtown streets among yawnably evergreen melaleucas and Australian willows.
As a species, sweetgum has the further virtue of producing mutant offspring with advantages for urban use. From one rebellious orange-headed tree on Palo Alto’s Bryant Street came the ‘Palo Alto’, a cultivated variety much used in California. Among other cultivars are the ‘Burgundy’, with fall foliage of that color, ‘Variegata’ or ‘Gold Dust’, its green leaves streaked with yellow, and the cold-hardy ‘Moraine’, a speedy, uniform grower with wine fall foliage.
THE SPINY SIDE
If the sweetgum is such a star, why doesn’t every city in North America give it top billing? For one thing, it’s a star that shuns the most frigid circuits. It sets its natural limits at Danbury, Conn., in New England, and southern Illinois in the Midwest. True, some icy towns in Massachusetts, Maine, Ontario, and elsewhere try their luck with the tree. But they work with stock from the northernmost range or the cold-hardiest cultivated varieties. At about -35°F, however, just about any sweetgum will call it quits.
Male sweetgum flowers.
But why should cities such as Sunnyvale, Calif., blacklist sweetgum as a street tree? The answer is in the unusual fruit, which some communities consider a liability. Like the American sycamore’s “buttonball,” the sweetgum fruit is a ball-shaped cluster of seeds and seed-dispensing apparatus. But unlike the soft sycamore ball, the sweetgum fruit ripens into a woody sphere covered with projecting hooked beaks. The beaks—each pair originally female parts of the flower—are now the tips of seed-containing capsules. In fall, the beaks open and winged seeds fall out. The “gumballs” remain on the tree through much of winter; but when they fall en masse and roll along the ground to disperse more seeds, they can spike a bare foot or twist an ankle as quickly as citizens can holler “Lawsuit!”
Thus many a nervous urban forester dismisses the sweetgum tree as a “litterer”—a snub that irritates those who find wonder, not bother, in a tree’s intricately engineered mechanisms. “There is … no justification for simply eliminating such species of trees from city planting,” says landscape architect Henry F. Arnold. “There are places where their special characteristics far outweigh the inconvenience of removing the organic litter.”
Cultivators have developed a fruitless sweetgum, but at the price of a winter delight. The sweetgum’s seed balls are fruits with character, bobbing like miniature maces from the tree’s bare branches. Children like collecting them; craftspeople gild them as decorations. Clever gardeners use them as cat-resistant mulch.
Often, but not always, sweetgums come up with still another visual treat: corky wings or quirky growths of bark along the branchlets and twigs. In the late 1800s, New York peddlers offered these branchlets as “alligator plants.” Neither plant nor alligator is known to have sprouted from them.
Some sweetgum twigs develop corky wings and an “alligator” look.
For all its merits, the American sweetgum seems to have been a lost cause of statesman Alexander Hamilton, who had a passel of lost causes before losing his life in a duel. Hamilton, reportedly, was so enamored of the sweetgum that he wished it to become the nation’s emblematic tree. It did not happen, nor, surprisingly, is the sweetgum the official tree of any state. However, about 80 miles east of the Alabama state capital (Montgomery), in a bucolic region of rolling hills and dense forests, sits the proud town of Crawford, population 650. Its official tree, Hamilton might be pleased to know, is one with aromatic resin, striking fall color, and a star-shaped leaf.