The Sweet Gum tree (Liquidambar styraciflua) is a deciduous shade tree recognized across the eastern United States for its star-shaped leaves and brilliant fall colors. While the foliage is admired, the reproductive structure often captures attention or causes annoyance when it falls. The hard, spiky objects that drop are fruit capsules, not the true seeds. The actual seeds are tiny components released from these protective outer shells, serving as the biological unit for the tree’s propagation.
The Distinctive Seed Capsule
The most commonly encountered structure is the fruit capsule, often called a “gumball.” These woody, spherical aggregates measure approximately 1 to 1.5 inches (2.5–3.8 cm) in diameter. They mature throughout the summer and fall, transitioning from green to a dry, brown or gray color as they ripen in late autumn.
The surface of the fruit is covered in sharp, prickly points, leading to its reputation as a nuisance when it litters the ground. The gumball is a cluster of multiple tiny, hard compartments. As the capsule dries, it develops small slits or pores, allowing the seeds housed inside to be released. These empty, woody structures often persist on the branches throughout the winter before finally dropping.
Identifying the True Seed
The true sweet gum seed is found inside the woody capsule compartments and differs drastically from the prickly outer shell. Each mature capsule can hold 50 or more seeds, with viable seeds measuring less than a quarter of an inch in length. Fertile seeds are flat, dark (black or reddish-brown), and possess a small, membranous wing on either side. This wing structure aids in dispersal once the seed is released.
Not all material released from the capsule is capable of germination. The capsule also releases a large amount of infertile material, often called chaff. This sterile matter is yellow or light tan, lacks the dark color and distinct wing of the fertile seed, and looks like fine sawdust. A single gumball may disseminate an average of 56 viable seeds, though this number can be lower.
Natural Role of Sweet Gum Seeds
The small, winged structure is a physical adaptation that facilitates wind dispersal. Once the mature capsules open in late fall and winter, the seeds are released and carried away from the parent tree by air currents. While dispersal can extend hundreds of feet, most seeds land within a few hundred feet of the original tree.
The seeds are an important food source for numerous species of wildlife, especially during colder months when other food sources are scarce. At least 25 species of birds, including goldfinches, sparrows, mourning doves, and wild turkeys, consume the seeds. Small mammals, such as squirrels and chipmunks, also forage for the seeds, often accessing them directly from the fallen capsules.