American sweetgum (Liquidambar styraciflua, L. 1753)

Identity

American sweetgum (Liquidambar styraciflua L., 1753), also known as sweetgum or redgum, is a large deciduous tree in the genus Liquidambar, its only representative native to the Americas. Long placed in the Hamamelidaceae, it is now assigned to the Altingiaceae family. ^{1 4}

The genus name combines Latin liquidus (“fluid”) with Arabic al-'anbar (“amber”). Linnaeus coined it in 1753, referring to the fragrant resin released by damaged bark. Two centuries earlier, in 1517, the conquistador Juan de Grijalva had observed Maya offerings of this fragrance in hollow reeds filled with dried herbs and liquidambar and burned as offerings. ¹⁰

Recognition

Cultivated trees commonly reach 15–20 m (49–66 ft), while wild specimens have been recorded at 45 m (148 ft). Trunks average 60–90 cm (24–35 in) in diameter. A pyramidal crown becomes more oval as the tree ages and its branches gain weight. ^{4 10}

The star-shaped leaves are alternate, unlike the opposite leaves of maples. They have five pointed lobes, sometimes three or seven, measure 8–13 cm (3–5 in) across, and have stalks 6–10 cm (2.4–4 in) long. Crushed leaves release a faint resinous scent associated with their tannin content. In fall they turn yellow, orange, red and purple, often on the same tree. ⁴

Light brown to gray bark develops deep fissures and irregular plates, giving rise to the name alligatorwood. Young branches develop winglike corky ridges from their second year, a feature that adds weight to the crown under snow or ice. ⁴

Useful taxonomy

POWO/WCVP accepts the name Liquidambar styraciflua L. Several historical synonyms and varietal names still appear in literature and the nursery trade:

• Liquidambar gummifera Salisb., nom. superfl., a historical synonym
• Liquidambar macrophylla Oerst.
• Liquidambar styraciflua var. mexicana Oerst.
• Liquidambar styraciflua f. rotundiloba Rehder

The related Turkish species Liquidambar orientalis historically supplied the true commercial styrax. Earlier confusion between the two trees explains why “storax” was applied to both resins. Of the five Liquidambar species distributed across the Americas, Asia and the Mediterranean region, L. styraciflua is the only one native to the Americas. ¹

Habitat and range

Native populations occupy the eastern and south-central United States, from Connecticut to Texas and Florida, in moist lowlands. Farther south, the range resumes from Nuevo León in Mexico through Guatemala, Honduras, Nicaragua, El Salvador and Belize. There it grows in cloud forests at middle elevations, under humid, relatively mild tropical mountain conditions. ^{7 4}

The IUCN assesses Liquidambar styraciflua as Least Concern. Its broad, continuous range supports that status despite substantial timber harvesting in the southeastern United States. ⁵

Planting beyond the native range has made American sweetgum a familiar ornamental in parks and streets across Europe, including France, and in Colombia and Australia. It is not considered invasive in these locations. ⁶

Life cycle and reproduction

Spring brings male and female flowers on the same tree, making the species monoecious. Male flowers form terminal clusters 5–8 cm (2–3 in) long, while female flowers form solitary heads. Small, greenish and without petals, both are easily overlooked. ⁴

Pollination produces a spherical, spiny compound fruit 3–4 cm (1.2–1.6 in) across, made of 40–60 fused capsules, each with two points. These gumballs remain on the branches through winter before falling abundantly to the ground. ⁴

Winged seeds disperse on the wind and germinate after 30–90 days of cold stratification at 1–5 °C (34–41 °F), or soaking for 15–20 days. In favorable soil, a young tree takes 20–30 years to develop its mature crown and reach full fruit production. ¹⁰

Uses and risks

Reddish-brown timber, sometimes streaked with black, makes this one of the southeastern United States' most important commercial hardwoods. Uses include plywood, furniture, crates, barrels and even chopsticks for Asian markets. The wood takes a good polish but warps readily during drying. ⁴

Resin known as liquidambar or sweetgum balsam comes from wounded bark and is recovered through incision, boiling and pressing. Traditionally used in Chinese medicine for coughs and diarrhea, it has also attracted research as a renewable source of shikimic acid, a precursor for antiviral synthesis. Fruit extracts are being studied for potential anticancer activity; these are research interests rather than established treatments. ^{8 9}

American sweetgum is not toxic to people or domestic animals. Its main hazards are physical: fallen spiny fruits roll underfoot and damage lawns, while surface roots can lift sidewalks and affect foundations in compacted soil. NC State recommends allowing more than 18 m (59 ft) of available space before planting. ⁴

Varieties, look-alikes and related plants

RHS Award of Garden Merit selections include 'Worplesdon', with deeply cut leaves and orange, red and purple fall colors, alongside 'Lane Roberts' and 'Penwood'. Sterile 'Rotundiloba', with rounded leaf lobes, was selected in North Carolina in the 1930s to eliminate spiny fruits. The dwarf 'Gumball', rarely exceeding 2 m (6.6 ft), suits smaller gardens. ^{2 3}

Star-shaped foliage resembles that of maples (Acer), but American sweetgum's alternate leaves immediately distinguish it from their opposite pairs. Its round fruits also recall American sycamore (Platanus occidentalis). Unlike the sycamore's soft fruiting heads, which break apart at maturity, sweetgum fruits remain hard, spiny and intact long after falling.

Main sources

• Plants of the World Online / Kew, Liquidambar styraciflua L.
• Royal Horticultural Society, Liquidambar styraciflua 'Worplesdon'
• Royal Horticultural Society, AGM Plants — Ornamentals list (2017)
• NC State Extension Gardener Plant Toolbox, Liquidambar styraciflua
• IUCN Red List, Liquidambar styraciflua assessment (Beech et al., 2018)
• INPN / MNHN, Liquidambar styraciflua — American sweetgum
• Atlas of Florida Plants (University of South Florida), Liquidambar styraciflua
• Enrich et al., 2008, Liquidambar styraciflua — a renewable source of shikimic acid, Tetrahedron Letters
• Pozzobon et al., 2023, chemical evaluation of Liquidambar styraciflua fruit extracts, Molecules
• Cal Poly Plant Conservatory (archived), Liquidambar styraciflua — American sweet gum