Latin name: Liquidambar styraciflua
Common names: Sweet gum tree, American sweetgum, Redgum
Two forms of Sweet gum tree are recognised in horticulture: the round-lobed American sweet gum, L. styraciflua forma rotundiloba; and the Weeping American sweet gum, L. styraciflua forma pendula
Sweet gum is native to North America and to scattered locations in northeastern and central Mexico, Guatemala, Belize, El Salvador, Honduras, and Nicaragua. Sweet gum has been introduced into California as well as southwestern British Columbia (1-2). It is now found planted all over the world.
Sweet gum is a large, long-lived, deciduous hardwood tree that grows 15 to 45 m in height. The bark is grey-brown and deeply, irregularly furrowed into narrow, scaly plates or ridges. Young Sweet gum trees have long conical crowns, while mature trees have crowns that are round and spreading. The tree is easily recognised by the long-petioled, star-shaped leaves, which have 5 long-pointed, saw-toothed lobes. In autumn the leaves turn various shades of red and yellow.
Sweet gum flowers appear from March to May. The tree is monoecious (individual flowers are either male or female, but both sexes can be found on the same plant), with the male flowers in several clusters on an upright raceme, and the female flowers borne on a slender stalk. Both kinds of flower are small, green in colour, and inconspicuous.
The brown, ball-shaped fruits ("gumballs"), 2.5 to 4 cm in diameter, ripen from September to November and persist throughout the winter. Sweet gum produces an abundance of lightweight seed. The seed is winged and dispersed by wind, mainly within 60 m but sometimes travelling up to 180 m away.
Sweet gum grows best on alluvial clay and loamy soils of river bottoms, but tolerates a wide variety of conditions.
Sweet gum is valued as a lawn and park tree, and is quite showy in the fall (1). But the tree is primarily used for lumber, veneer, and plywood.
Medicinally, Sweet gum is known as "Copalm balsam"; the resinous gum is used extensively in Mexico and Europe as a substitute for storax. Ointments and syrups are made from it. It is also used as a perfuming agent in soap.
No allergens from this plant have yet been characterised.
An extensive cross-reactivity among the different individual species of the genus could be expected (3).
Sweet gum tree produces great quantities of anemophilous pollen, and although anecdotal evidence of allergic sensitisation has been reported, few cases have been documented. Some authors have felt that Sweet gum is a minor cause of hay fever (4-5), whereas others (6) have commented on its profuse pollen production and presented data on significant skin sensitisation in 325 patients in Alabama, California, and Florida. Asthma has not been reported (1).
In a study in Westchester County in the state of New York, out of 100 patients referred for allergic rhinitis, 65% had a positive skin prick test to at least 1 aeroallergen out of 48 in the test panel. Sweet gum was positive in 16 (7).
Compiled by Dr Harris Steinman, email@example.com.
Weber RW. Liquidambar styraciflua.
Ann Allergy Asthma Immunol 2003;90(6):A6
Farrar JL. Trees of the Northern United States and Canada, Ames,IA: Iowa State University Press, 1995:240-1
Yman L. Botanical relations and immuno-logical cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
Wodehouse RP. Hayfever Plants. Waltham, MA:
Chronica Botanica, 1945:167
Wodehouse RP. Pollen Grains: Their Structure, Identification and Significance in Science and Medicine. New York, NY: McGraw-Hill, 1935:425-7
Lewis WH, Vinay P, Zenger VE. Airborne and Allergenic Pollen of North America. Baltimore, MD: Johns Hopkins University Press, 1983:58-61.
Basak P, Arayata R, Brensilver J Prevalence of specific aeroallergen sensitivity on skin prick test in patients with allergic rhinitis in Westchester County. Internet J Asthma Allergy Immunol 2008; 6(2)