The term “spiky balls” most often refers to the fallen fruit of the American sweetgum tree, a common sight in urban and suburban landscapes across North America. While several tree species produce similar prickly seed capsules, the sweetgum is the most frequent source of these sidewalk hazards. Identifying the tree responsible requires examining the specific characteristics of the fruit and the leaves.
The Primary Culprit: Sweetgum Trees
The tree most commonly associated with the persistent, hard, spiky spheres is the American sweetgum (Liquidambar styraciflua). Its distinctive fruit is a woody, spherical capsule, roughly 1 to 1.5 inches in diameter, covered in stiff, pointed projections. These fruits, colloquially called “gumballs,” mature in autumn but often persist on the tree through winter before dropping in large numbers.
The sweetgum is easily identifiable by its unique foliage, which features star-shaped leaves with five to seven sharply pointed lobes. This distinct leaf shape is unlike the compound leaves of other similar trees. The tree is native to the eastern United States, ranging from New York down to Florida and extending west into Texas, thriving in USDA Hardiness Zones 5 through 9. The seeds within the gumballs are a food source for small songbirds, such as finches and chickadees, during the winter months.
Differentiating Other Spiky Producers
While the sweetgum is the primary source, other trees produce spiky or burr-like fruits that can cause confusion. Members of the Aesculus genus, including the Ohio buckeye (Aesculus glabra) and the common horse chestnut (Aesculus hippocastanum), are prominent examples. The fruit of these trees is a round, leathery husk often covered in softer, less rigid spines compared to the sweetgum’s woody points.
A major distinguishing factor is the fruit’s interior. Buckeye and horse chestnut husks split open into two to four valves to release a single, large, smooth, dark brown nut, which is highly toxic to humans. Conversely, the sweetgum ball remains intact and releases numerous small, winged seeds through tiny openings between the spikes. Buckeye and horse chestnut leaves are palmately compound, meaning multiple leaflets radiate from a central point, a structure different from the sweetgum’s simple, star-shaped leaf.
The Botanical Purpose of the Spiky Fruit
The evolution of spiky capsules serves a dual function in the tree’s life cycle: seed protection and dispersal. The hard, woody shell and sharp projections act as a deterrent to most seed predators, such as squirrels and insects, while the seeds are developing. By making the fruit difficult to chew and access, the tree increases the likelihood that its seeds will survive to maturity.
For dispersal, the spikes on the sweetgum fruit are instrumental in keeping the capsule from being washed away by water once it falls. The projections also allow the balls to roll away from the parent tree or latch onto the fur of passing animals, carrying the seeds to new locations. Each sweetgum ball is a complex structure made up of many two-celled capsules, each holding two tiny seeds that are released slowly from fall into winter.
Management and Uses of the Spiky Balls
For many property owners, the dense litter of sweetgum balls is considered a nuisance due to the constant cleanup required and the tripping hazard they pose on paved surfaces. When stepped on or run over by a lawnmower, the hard, spiky balls can be propelled at high speeds. One management approach is to plant non-fruiting cultivars, such as ‘Rotundiloba,’ which do not produce the troublesome gumballs.
Beyond the inconvenience, the American sweetgum tree yields valuable timber, often sold commercially as red gum or satin walnut. The fruit also has niche uses; the spiky balls are sometimes collected for crafts, holiday decorations, or as a natural mulch that deters slugs and cats from garden beds. Historically, the fruit has been a source of shikimic acid, a compound used in the production of antiviral medications.