Liquidambar, commonly called sweetgum (sweet gum in the UK), gum, redgum, satin-walnut, or American storax, is the only genus in the flowering plant family Altingiaceae and has 15 species. They were formerly often treated in Hamamelidaceae. They are decorative deciduous trees that are used in the wood industry and for ornamental purposes.
Temporal range: late Cretaceous - Recent
|Sweetgum (Liquidambar styraciflua)|
- Liquidambar acalycina – Chang's sweetgum (central & southern China)
- †Liquidambar changii - Miocene (Washington state, North America)
- Liquidambar formosana – Chinese sweetgum or Formosan sweetgum (central & southern China, southern Korea, northern Thailand, Taiwan, Laos, northern Vietnam).
- Liquidambar orientalis – Oriental sweetgum or Turkish sweetgum (southwest Turkey, Greece: Rhodes).
- Liquidambar styraciflua – American sweetgum (eastern North America from New York to Texas and also eastern Mexico to Honduras).
They are all large, deciduous trees, 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. Their leaves can be many colors such as bright red, Orange and yellow. 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 (0.79–1.57 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. Fall colors are most brilliant where autumn nights are chilly, but some cultivars color well in warm climates. Although a temperate species, at least one living Liquidambar tree survives in a hot and humid tropical city: Bangkok, Thailand.
Species within this genus are widespread in China, Korea, Thailand, Taiwan, Laos, Vietnam, Turkey, Rhodes, North America and Mexico up to Honduras). In cultivation they can be seen in warm temperate and subtropical climates around the world.
This genus is known in the fossil record from the Cretaceous to the Quaternary (age range: 99.7 to 0.781 million years ago). The genus was much more widespread in the Tertiary, but has disappeared from Europe due to extensive glaciation in the north and the east-west oriented Alps and Pyrenees, which have 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 Lepidoptera caterpillars, such as the gypsy moth. The American sweetgum is widely planted as an ornamental, within its natural range and elsewhere.
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 the 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 is claimed to promote 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.
The trees drop their hard, spiky seedpods in the fall by the hundreds, and these can become a serious nuisance on pavements and lawns. Some cities have expedited permitting for removal of liquidambar trees.
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