Liquidambar, commonly called sweetgum (sweet gum in the UK),gum,redgum,satin-walnut, or American storax, is a genus of five species of flowering plants in the family Altingiaceae, though formerly often treated in the Hamamelidaceae. They are all large, deciduoustrees, 25–40 metres (82–131 ft) tall, with palmately 3- to 7-lobed leaves arranged spirally on the stems and length of 12.5 to 20 centimetres (4.9 to 7.9 in), having a pleasant aroma when crushed. Mature bark is grayish and vertically grooved. The flowers are small, produced in a dense globular inflorescence 1–2 centimetres (0.39–0.79 in) diameter, pendulous on a 3–7 centimetres (1.2–2.8 in) stem. The fruit is a woody multiple capsule 2–4 centimetres (0.79–1.6 in) in diameter (popularly called a "gumball"), containing numerous seeds and covered in numerous prickly, woody armatures, possibly to attach to fur of animals. The woody biomass is classified as hardwood. In more northerly climates, sweetgum is among the last of trees to leaf out in the spring, and also among the last of trees to drop its leaves in the fall, turning multiple colors. Although a temperate species, at least one living Liquidambar tree survives in a hot and humid tropical city: Bangkok, Thailand.
The genus was much more widespread in the Tertiary, but has disappeared from Europe due to extensive glaciation in the north and the Alps, which has served as a blockade against southward migration. It has also disappeared from western North America due to climate change, and also from the unglaciated (but nowadays too cold) Russian Far East. There are several fossil species of Liquidambar, showing its relict status today.
The wood is used for furniture, interior finish, paper pulp, veneers and baskets of all kinds. The heartwood once was used in furniture, sometimes as imitation mahogany or Circassian walnut. It is used widely today in flake and strand boards. Sweetgum is a foodplant for various Lepidopteracaterpillars, such as the gypsy moth. The American Sweetgum is widely planted as an ornamental, not only within its natural range.
The hardened sap, or gum resin, excreted from the wounds of the Sweetgum, for example the American Sweetgum (Liquidambar styraciflua), can be chewed on like chewing gum and has been long used for this purpose in Southern United States. The sap was also believed to be a cure for sciatica, weakness of nerves, etc.
In Chinese herbal medicine, lu lu tong, or "all roads open," is the hard, spiky fruit of native sweetgum species. It first appeared in the medical literature in Omissions from the Materia Medica, by Chen Cangqi, in 720 AD. Bitter in taste, aromatic, and neutral in temperature, lu lu tong promotes the movement of blood and Qi, water metabolism and urination, expels wind, and unblocks the channels. It is an ingredient in formulas for epigastric distention or abdominal pain, anemia, irregular or scanty menstruation, low back or knee pain and stiffness, edema with difficult urination, or nasal congestion.