Sweetgums

Sweetgum (Liquidambar styraciflua L.): A Comprehensive Encyclopedic Reference

1. Identity: Botanical Classification, Names, and Natural Source

Liquidambar styraciflua L., commonly known as the American sweetgum, is a deciduous tree in the genus Liquidambar native to warm temperate areas of eastern North America and tropical montane regions of Mexico and Central America. It is currently classified in the plant family Altingiaceae, but was formerly considered a member of the Hamamelidaceae.

The genus name Liquidambar was first given by Linnaeus in 1753 from the Latin liquidus ('fluid') and the Arabic ambar ('amber'), in allusion to the fragrant terebinthine juice or gum which exudes from the tree. The specific epithet styraciflua is an old generic name meaning 'flowing with storax' (a plant resin). Its Nahuatl name is Ocotzocuahuitl, which translates as "tree that gives pine resin."

Other English names include Liquidambar, American Storax, American Sweetgum, Bilsted, White Gum, Red Gum (and Redgum), Star-leaved Gum, Starleaf Gum, Alligator Tree, and Alligatorwood.

There are four species of sweetgum including Liquidambar orientalis L. (L. orientalis), Liquidambar formosana Hance (L. formosana), Liquidambar styraciflua L. (L. styraciflua), and Liquidambar acalycina (L. acalycina) worldwide. However, only L. styraciflua is native to North America, where it has a widespread distribution across the southeastern United States, growing as far north as Connecticut, ranging south to Florida, and west as far as Texas, and also growing in Central America from Mexico to Panama.

This species has wide intercontinental distribution in the south and southeast of the United States, extending to Central America and Mexico, and has also been acclimated in the south and southeast of Brazil because of damp soils and frosts.

Common Forms and Preparations

• Storax (American Storax / Copalm Balsam): Many of the medicinal properties of sweetgum come from storax as well as essential oils extracted from the leaves. Storax, also referred to as styrax, is produced by damaging the outer bark of sweetgum trees; when the tree is wounded, the inner bark produces a balsam. Boiling the inner bark in water effectively removes the balsam and produces storax. Storax produced from L. orientalis, or Turkish sweetgum, is referred to as Asian storax, while storax derived from L. styraciflua is called American storax.
• Essential Oil: The essential oil of the plant has potential biological activity and has attracted considerable interest in the pharmaceutical industry. It is typically obtained by steam distillation of the leaves.
• Hydroalcoholic and Methanolic Extracts: Studies with this species have demonstrated antioxidant capacity, hepatoprotective activity, acetylcholinesterase enzyme inhibition, antitumor action, anti-inflammatory and antimicrobial activities, as well as synergism with antibiotics, evaluated mainly in alcoholic extracts (hydroalcoholic and methanolic) and essential oil of leaves, bark, and stem.
• Chewing Resin / Gum: The hardened gum or rosin from the tree was used as chewing gum: a piece of the bark was knocked from the tree, and after one week the sap from the wound had hardened and could be collected and used for chewing gum. Tea was also made from both the fruits and the bark.
• Seed Extracts: An isolation procedure yields 2.4–3.7% w/w pure shikimic acid from the seeds of Liquidambar styraciflua. Shikimic acid, the starting material in the commercial synthesis of the antiviral agent oseltamivir and an important intermediate in the biosynthesis of aromatic amino acids in plants, was found by HPLC to be abundant in the granular, aborted seeds (6.5% w/w) while present only in small amounts in the developed, fertile seeds (0.14% w/w).

2. Traditional and Historical Use

Early Historical Documentation

American Sweetgum was first documented in 1519 by Spanish explorer Bernal Diaz del Castillo, when he noted the Aztec Emperor Montezuma using the tree's resin. It also appears in 16th century Spanish-Mexican herbals, noted for treating illnesses and wounds such as skin issues, diarrhea, coughs, and dysentery, as the resin contains antimicrobial properties.

A journal from a conquistador accompanying Cortez recorded observing the Aztec emperor himself enjoying a resinous stick from the tree. The Spaniard recognized its similarity to the well-known Asian species (and close kin) that exuded the same resin. Spanish explorers of the American South also noted the resemblance and recorded the tree as they trudged through southern swamps. The first formal appearance of the tree in botanical literature was in the first Spanish-language Mexican herbal in the late 16th century.

Storax has medicinal uses dating back to the Aztec Empire during the Paleo-Indian Period (ca. 10,000–7000 BC). The ancient Aztecs collected the boiled-down, grayish-brown, sticky, opaque liquid and used it as a treatment for skin infections and other ailments. The Aztecs also reportedly chewed it as a gum and burned it as incense.

Indigenous North American Use

The sweetgum tree was used by the Cherokee, Choctaw, Koasati, Rappahannock, and other Native American tribes for various purposes. Various southeastern Indigenous nations, including the Cherokee, Choctaw, Chickasaw, and Natchez, used sweetgum resin as a topical antiseptic, wound treatment, and treatment for skin conditions. The resin was mixed with bear grease as a salve for skin ailments and applied to cuts and sores. The inner bark was used in preparations for treating fevers and dysentery.

The Cherokee utilized the sweet gum tree (bark/sap) as a diaphoretic, febrifuge, dermatological treatment, and as a general medicine. The Powhatan Indians utilized dried bark mixed with bark of Red Oak to make an infusion used to treat dysentery.

The storax and essential oils from the leaves of these trees present medicinal properties and have been used by Native Americans to treat inflammation, stomach pain, wounds, cough, bronchitis, enlarged liver, and amenorrhea.

Indigenous peoples, including the Cherokee and Choctaw, applied it as a salve for wounds and skin irritations, brewed it as an infusion to calm the nerves, and hardened it for use as a chewing gum.

Appalachian and Colonial Folk Medicine

Sweetgum sap was used for medicinal purposes: by mouth to treat diarrhea, topically as a salve for wounds, and as a tea to calm nervousness. Appalachian settlers made a concoction of resin and whiskey to clean teeth, heal gums and mouth lesions, and relieve toothache. As an expectorant, boiled and cooled sap was used to treat fevers, bronchial infections, and croup.

Early European colonists quickly adopted the resin's uses from Indigenous peoples. Storax was valued as a fumigant, a fixative in perfumery, an ingredient in medicines, and a treatment for skin conditions including ringworm and scabies.

Traditional Chinese Medicine

Traditionally, sweet gum has been used in Chinese medicine to treat issues such as diarrhea, coughs, and skin sores. In traditional Chinese medicine, L. styraciflua is used in the treatment of gastrointestinal disorders, such as diarrhea and dysentery, coughs, and skin sores.

Edible and Aromatic Uses

The resin from sweetgum is used as both a chewing gum and mouth freshener as well as a stabilizer for baked goods. Medicinally, the resin is used as an antiseptic, diuretic, expectorant, parasiticide, poultice, salve, sedative, and stimulant. An assortment of ailments treated using the resin include sore throat, cough, asthma, cystitis, wounds, and skin conditions.

3. Key Constituents and Active Compounds

Storax / Resin Constituents

The aromatic resin 'Storax' is obtained from the trunk of this tree. It forms in cavities of the bark and also exudes naturally. Several types of phytoconstituents have been isolated from the genus Liquidambar, including tannins, iridoids, flavonoids, di- and triterpenoids.

Phenolic Acids and Terpenes (Fruit Extracts)

Analyses of fruit extracts showed that a polysaccharide fraction contained pectic polysaccharides, such as acetylated and methyl esterified homogalacturonans together with arabinogalactan, while an ethanolic fraction presented phenolic acids and terpenes such as gallic acid, protocatechuic acid, liquidambaric acid, combretastatin, and atractyloside A.

Flavonoids and Polyphenols (Leaf Extracts)

The content of the main groups of biologically active compounds in the leaves has been analyzed, including flavonoids (catechins, leucoanthocyanins, anthocyanins), vitamins (ascorbic acid), pigments (carotenoids, chlorophylls), polysaccharides, and tannins. Flavonoid compounds in the leaves of L. styraciflua were found to contain 356.13 mg% of catechins, 151.86 mg% of anthocyanins, and 872.93 mg% of leucoanthocyanins.

Earlier studies on the secondary metabolites of L. styraciflua reported the isolation of gallic and ellagic acids, shikimic acid, as well as triterpenoids. Moreover, its cytotoxic, cancer chemopreventive, and antihypertensive effects have been evaluated.

Essential Oil Constituents

The essential oil composition was analyzed using gas chromatography and mass spectrometry. The main compounds were α-pinene (43.7%), β-pinene (10.7%), d-limonene (35.3%), and terpinen-4-ol (10.3%). Altogether, 64 volatile secondary metabolites were identified. The major components of the leaf oil were d-limonene, α-pinene, and β-pinene, while the stem oil contained primarily germacrene D, α-cadinol, d-limonene, α-pinene, and β-pinene.

Sesquiterpenes, including β-caryophyllene, germacrene D, and α-/δ-cadinol, constitute approximately 25.5% of the stem oil compared with approximately 10% in the leaf oil during summer.

Shikimic Acid

In addition to the sap, the leaves, bark, and seeds of sweetgum also possess beneficial compounds such as shikimic acid, a precursor to the production of oseltamivir phosphate, the active ingredient in Tamiflu® — an antiviral drug effective against several influenza viruses. Specifically, L. styraciflua contains shikimic acid in its leaves, bark, and young seeds, making Liquidambar species valuable resources that can effectively inhibit the H1N1 virus through this precursor relationship.

Total Phenolic Content

The ethanolic subfraction (S-EA) of fruit extracts presented the highest level of phenolic compounds at 298.4 mg/g of extract. Other authors evidenced the presence of phenolic compounds with values of 111.5 mg GAE/g extract for methanol extraction of the leaves of L. styraciflua, while extractions with other solvents provided higher contents of phenolics, such as 1614.02 ± 0.006 mg GAE/g extract with acetone and 1419.34 ± 0.033 mg GAE/g extract with ethanol extraction.

4. Scientific Evidence by Area of Use

4.1 Anti-Inflammatory Activity

A published study aimed to evaluate the variations in the chemical composition and bioactivity of essential oils of L. styraciflua collected in different seasons. The oils were analyzed by gas-liquid chromatography and mass spectrometry. Antioxidant activity was investigated by DPPH and superoxide anion radical scavenging assays and the deoxyribose degradation assay. Inhibition of both 5-lipoxygenase (5-LOX) and prostaglandin E2 (PGE2) production in hepatic cancer (HepG-2) cells were used to assess the anti-inflammatory activity, and cytotoxic activity was investigated using the MTT assay.

The essential oils of L. styraciflua exhibited an interesting anti-inflammatory activity with low cytotoxicity, supporting its traditional use to treat inflammation.

According to Mancarz et al., the extracts of stem and leaves of this plant showed a great anti-inflammatory response by inhibiting the hyaluronidase enzyme compared to commercial propolis extract. Their results showed that the butanolic fraction and hydroalcoholic extract of L. styraciflua stems were responsible for this marked anti-inflammatory effect.

The essential oil exhibited good anti-inflammatory activity in a concentration-dependent manner, evaluated using a hyaluronidase enzyme inhibition assay.

Evidence strength: All anti-inflammatory evidence to date is preclinical — derived from in vitro enzyme inhibition assays and cell culture models. No human clinical trials have been conducted to confirm anti-inflammatory efficacy in people.

4.2 Antimicrobial Activity

The sap, known as storax, has been used for centuries to treat common ailments such as skin problems, coughs, and ulcers. More recently, storax has proven to be a strong antimicrobial agent even against multidrug resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA).

Using an agar diffusion method where 100 µl of extract at a concentration of 4 mg/ml in ethanol was added to the well, it was observed that the leaf extract was an effective antimicrobial against several strains of pathogenic bacteria with zones of inhibition ranging from 10 mm to 34 mm. The affected bacteria included P. vulgaris (zone of inhibition = 34 mm), P. fluorescens (22 mm), Salmonella typhimurium (22 mm), S. aureus (20 mm), as well as multidrug-resistant S. aureus (MRSA, 20 mm).

A synergistic interaction was observed against the Gram-positive bacteria Enterococcus faecalis (hydroalcoholic extract of leaves combined with tetracycline) and Staphylococcus aureus (hydroalcoholic extract of stem combined with tetracycline).

The essential oil of Liquidambar styraciflua leaf, which includes α-pinene as its major compound, also showed a good synergistic effect with tetracycline and ciprofloxacin against Bacillus subtilis (ATCC 6633).

Evidence strength: Antimicrobial activity has been demonstrated consistently in multiple in vitro studies, including against drug-resistant pathogens. However, all available evidence is preclinical (laboratory-based); no human clinical trials have assessed the antimicrobial utility of sweetgum preparations in treating infectious disease.

4.3 Antioxidant Activity

The fruit extracts showed antioxidant activity, with IC50 values of 4.64 µg/mL, 16.45 µg/mL, and 3.67 µg/mL for the whole aqueous extract, the polysaccharide fraction, and the ethanolic subfraction, respectively.

Several studies have correlated the presence of phenolic compounds with antioxidant activity because of their capacity to capture free radicals, thus preventing some diseases such as cardiovascular and degenerative disorders, as well as cancers.

Evidence strength: Antioxidant activity has been repeatedly confirmed by in vitro radical scavenging assays (DPPH, ABTS, FRAP methods) across multiple studies. No human clinical trials have verified in vivo antioxidant benefit.

4.4 Hepatoprotective Activity

The methanolic extract of the leaves of L. styraciflua (LSE) was evaluated for hepatoprotective and antioxidant activities in carbon tetrachloride (CCl4) liver-damaged rats. Hepatotoxicity was induced via intraperitoneal injection of CCl4 in olive oil at a dose of 0.5 ml/kg body weight. The animals received the extract orally at two dose levels (250 and 500 mg/kg body weight), and the administration regimen was twice a week for six consecutive weeks. LSE exhibited a significant dose-dependent protective effect by lowering serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), malondialdehyde (MDA), and ameliorating the level of serum protein. The above findings suggested that LSE could be considered as a standardized herbal product with antifibrotic, hepatoprotective, and antioxidant potential.

Evidence strength: Hepatoprotective evidence is limited to an animal model (rat CCl4-induced liver damage). No human or clinical studies are available. Results are preliminary and cannot be extrapolated to humans.

4.5 Antiviral Activity and Shikimic Acid as an Oseltamivir Precursor

The key ingredient in Tamiflu® is oseltamivir phosphate, of which shikimic acid is a precursor. Chinese star anise was the initial source of shikimic acid used for the production of this drug; however, much of the shikimic acid now manufactured is generated by a shikimic acid-producing E. coli, although some still comes from plant sources. Sweetgum trees, mainly L. styraciflua, were found to contain shikimic acid in their leaves, bark, and young seeds.

The shikimic acid obtainable from Liquidambar fruit coatings and leaves is approximately 3–8% on a dry basis depending on species, and with appropriate processing can be obtained at 98% purity and 70% yield. This method is being actively exploited in the Chinese industry for the production of shikimic acid from Liquidambar genus plants. Oseltamivir, commercialized under the trade name Tamiflu, is an antiviral drug synthesized from shikimic acid.

Research indicates potential antiviral properties in the resin and fruit extracts, including inhibition of H1N1 influenza neuraminidase (IC50 ≈ 102 µg/mL), underscoring shikimic acid's indirect contribution to antiviral therapies alongside direct inhibitory mechanisms. These findings suggest promising therapeutic avenues, though clinical trials in humans remain limited.

Evidence strength: The connection between L. styraciflua and antiviral therapy is primarily through its role as a renewable source of shikimic acid for pharmaceutical synthesis of oseltamivir. The shikimic acid itself is not the antiviral — it is a chemical precursor. Direct antiviral evidence from sweetgum extracts is limited to in vitro neuraminidase inhibition assays. No clinical trials exist for sweetgum as an antiviral agent in humans.

4.6 Anticancer / Cytotoxic Activity

The cytotoxicity of fruit extracts followed the sequence of the ethanolic subfraction being greater than the whole aqueous extract, which was greater than the polysaccharide fraction, demonstrating that the toxic compounds were separated from the non-toxic ones by ethanol precipitation. While the ethanolic subfraction is very toxic to any cell line, the polysaccharide fraction is a promising candidate for studies against cancer due to its high toxicity to tumoral cells and low toxicity to normal cells.

Earlier studies reported the biological effects of this species, including cancer chemopreventive (Fukuda et al., 2005), antihypertensive (Ohno et al., 2008), and cytotoxic activities in cancer cell lines (Elsayed et al., 2015).

The compound tentatively identified as combretastatin — from a group of natural phenols — was identified in fruit extracts of L. styraciflua.

Evidence strength: All anticancer evidence is preclinical, based on cell line (in vitro) cytotoxicity studies. No human clinical trials on L. styraciflua extracts as anticancer agents have been published. Findings are exploratory.

4.7 Acetylcholinesterase Inhibition (Cognitive/Neurological Interest)

Studies with this species have demonstrated acetylcholinesterase enzyme inhibition, which is of interest in the context of cognitive and neurological diseases. This activity has been documented in laboratory-based enzyme assays. No human studies have evaluated cognitive outcomes.

Evidence strength: Preclinical, in vitro only. No clinical data available.

4.8 Antihypertensive Effects

The antihypertensive effects of L. styraciflua have been evaluated in preclinical research settings. The phenolic and polyphenolic content of the plant is associated with vasodilatory mechanisms in vitro, though no controlled human studies have confirmed antihypertensive efficacy.

Evidence strength: Preclinical only. No human clinical data.

5. Body Systems and Health Areas

• Integumentary (Skin) System: Topical antiseptic, wound treatment, and treatment for skin conditions. The resin was mixed with bear grease as a salve for skin ailments and applied to cuts and sores.
• Respiratory System: Ailments treated using the resin include sore throat, cough, and asthma. As an expectorant, boiled and cooled sap was used to treat fevers, bronchial infections, and croup.
• Gastrointestinal System: In traditional Chinese medicine, L. styraciflua is used in the treatment of gastrointestinal disorders, such as diarrhea and dysentery.
• Hepatic (Liver) System: Preclinical studies demonstrate dose-dependent hepatoprotective and antifibrotic effects in animal models of CCl4-induced liver damage.
• Immune / Antimicrobial: More recently, storax has proven to have antibacterial properties and is effective even against multidrug resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA).
• Antiviral / Influenza: The leaves, bark, and seeds of sweetgum possess shikimic acid, a precursor to the production of oseltamivir phosphate, the active ingredient in Tamiflu® — an antiviral drug effective against several influenza viruses.
• Neurological System (Exploratory): Acetylcholinesterase inhibition activity has been reported in vitro, suggesting potential interest in neurological disorders, though this is purely preliminary.
• Cardiovascular System (Exploratory): Antihypertensive effects have been evaluated in preclinical research.
• Oral Health: Appalachian settlers made a concoction of resin and whiskey to clean teeth, heal gums and mouth lesions, and relieve toothache. The resin has also been chewed and used as a tooth cleaner.

6. Dosage Forms and Reported Dosages

There are no standardized or approved clinical dosage recommendations for sweetgum (L. styraciflua) preparations. Clinical trial data are lacking to recommend use for any indication, and there is no clinical evidence to support dosing recommendations. The following dosages appear only in preclinical (animal and in vitro) research literature:

• Hepatoprotective animal study (Eid et al., 2015): The methanolic extract of the leaves of L. styraciflua was evaluated in carbon tetrachloride liver-damaged rats. Hepatotoxicity was induced via intraperitoneal injection of CCl4 in olive oil at a dose of 0.5 ml/kg body weight. The animals received the extract orally at two dose levels (250 and 500 mg/kg body weight), and the administration regimen was twice a week for six consecutive weeks.
• Antimicrobial in vitro study: Using an agar diffusion method where 100 µl of extract at a concentration of 4 mg/ml in ethanol was added to the well, antimicrobial activity against several bacterial strains was assessed.
• Shikimic acid extraction yield: An isolation procedure yields 2.4–3.7% w/w pure shikimic acid from the seeds of Liquidambar styraciflua. Shikimic acid was found to be abundant in the granular, aborted seeds (6.5% w/w) while present only in small amounts in the developed, fertile seeds (0.14% w/w).
• Storax (topical): In vitro studies evaluating storax have demonstrated antibacterial and anti-inflammatory activities, and storax is used as a skin protectant and flavoring agent, as well as in perfumery.

7. Safety Considerations and Interactions

General Safety from Research Studies

The IC50 values obtained for extracts in one study indicated the absence of toxicity and only moderate cytotoxicity for the hydroalcoholic extract of the stem. On the basis of those findings, L. styraciflua may be considered as a potential therapeutic source with high anti-inflammatory activity and synergistic interactions with antibiotics against bacteria.

Differential Cytotoxicity of Fractions

The cytotoxicity of different fruit extract fractions differed substantially, demonstrating that toxic compounds were separated from non-toxic ones by ethanol precipitation. While the ethanolic subfraction is very toxic to any cell line, the polysaccharide fraction is a promising candidate for studies against cancer due to its high toxicity to tumoral cells and low toxicity to normal cells. This indicates that different preparations derived from sweetgum may carry very different toxicity profiles, and the preparation method is critical.

Topical Sensitization Risk

Allergic rhinitis has been reported in association with storax exposure. The resin carries a moderate risk of skin sensitization and should be used with caution on hypersensitive or damaged skin.

Drug Synergy and Interaction Potential

Synergistic interaction was observed with tetracycline against Enterococcus faecalis (hydroalcoholic extract of leaves) and Staphylococcus aureus (hydroalcoholic extract of stem). While in vitro synergism with antibiotics may be of therapeutic interest, it also raises the possibility that sweetgum preparations could potentiate or interact with antibiotic regimens.

Lack of Clinical Safety Data

Contraindications for storax have not been identified in the published literature. However, information regarding safety and efficacy in pregnancy and lactation is lacking, and use is to be approached with caution.

Pollen Allergy

Sweetgum is a wind-pollinated tree and its airborne pollen is a documented seasonal allergen. This is a separate consideration from the medicinal use of its resin or extracts, but individuals with established sweetgum pollen allergy may wish to exercise caution with preparations derived from the tree.

Overall Evidence Assessment

In vitro studies evaluating storax have demonstrated antibacterial and anti-inflammatory activities. Storax is used as a skin protectant and flavoring agent, as well as in perfumery. However, clinical trial data are lacking to recommend use for any therapeutic indication. These findings suggest promising therapeutic avenues, though clinical trials in humans remain limited. The body of evidence for L. styraciflua is predominantly preclinical — composed of in vitro assays and animal studies — and no well-designed randomized controlled trials in human subjects have been published for any of the health areas discussed above.

References

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• El-Readi MZ, et al. "Variations of the chemical composition and bioactivity of essential oils from leaves and stems of Liquidambar styraciflua (Altingiaceae)." Journal of Pharmacy and Pharmacology, 2013. PubMed 24117424
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