Rhus glabra (Smooth Sumac): A Comprehensive Reference
1. Identity, Taxonomy, and Botanical Description
1.1 Nomenclature and Taxonomy
Rhus glabra, the smooth sumac (also known as white sumac, upland sumac, or scarlet sumac), is a North American species of sumac in the family Anacardiaceae. The binomial authority is Rhus glabra L., meaning it was formally described by Carl Linnaeus. The genus Rhus L. (family Anacardiaceae) comprises more than 250 species of shrubs and trees distributed across temperate and tropical regions of the world. Within this large genus, R. glabra is the only sumac species native to all 48 contiguous states of the U.S.
The scientific name Rhus glabra comes from Greek — rhus is derived from "rhous," which means bushy sumac, while glabra means smooth and refers to the stem and leaves of the plant. The USDA Fire Effects Information System records the documented scientific name as Rhus glabra L. (Anacardiaceae). Additional synonyms encountered in the older literature include Rhus glabrum (a variant spelling used in early pharmacopeial entries).
Common names recognized in official and historical sources include smooth sumac, scarlet sumac, upland sumach, and Pennsylvania sumach. Other vernacular names appearing in period literature include vinegar tree and shoe-make.
1.2 Morphological Description
Smooth sumac has a spreading, open habit, growing up to 3 metres (10 ft) tall. The bark is smooth and gray to brown. The leaves are alternate, 30–50 centimetres (12–20 in) long, compound with 11–31 oppositely paired leaflets. Each leaflet is 5–13 cm (2–5 in) long, with a serrated margin. The leaves turn scarlet in the fall.
The species is dioecious. The flowers are tiny, green, produced in dense erect panicles 10–25 cm (4–10 in) tall, in the spring, later followed by large panicles of edible crimson berries that remain throughout the winter. The drupes or berries only are official in pharmacopeial terms. They should be gathered before the rains have removed their external downy efflorescence, for when this is washed off the berries are no longer acid.
1.3 Geographic Range and Habitat
It is native to North America, from southern Quebec west to southern British Columbia in Canada, and south to northern Florida and Arizona in the United States and Tamaulipas in northeastern Mexico. Smooth sumac is distributed widely throughout most of the contiguous U.S. and into Mexico. It does not occur in California. In Canada it extends from Lake Huron to central British Columbia.
1.4 Commercially Available Preparations and Dosage Forms
Historically, Rhus glabra was prepared in several standardized forms documented in official compendia. Fluidextractum Rhois Glabrae was official in the U.S. Pharmacopeia VIII (U.S. VIII), but then deleted. It was admitted to the National Formulary IV with a slight alteration in the menstruum. The fluidextract affords an excellent astringent in relaxing diarrheas and other conditions where the tannin drugs are useful.
Additional traditional forms recorded in the literature include decoctions of root bark, infusions of leaves and roots, powders applied as poultices, syrups prepared from the berries, medicinal wines, and concentrated extracts used as gargles. Sumach leaves have also been used in tanning, and a concentrated decoction of the bark is used as a mordant for dyeing red colors.
2. Traditional and Historical Use
2.1 Native American Ethnobotanical Use
Rhus glabra (Anacardiaceae) is a species used in folk medicine by North American native people. Ethnobotanical records show that Rhus glabra has been used for a multitude of purposes by North American indigenous peoples. Documentation comes from multiple tribal traditions:
- Cherokee: Red berries eaten for vomiting (antiemetic); infusion poured over sunburn blisters; infusion of bark taken to make human milk flow abundantly (galactagogue); red berries chewed for bedwetting (urinary aid); berries used to make black dye.
- Chippewa: Decoction of the growth that sometimes appears on the tree used for dysentery (antidiarrheal); infusion of roots taken for colds.
- Flathead: Infusion of green or dried branches taken for tuberculosis.
- Meskwaki: Berries and sugar used to make a cooling drink in the summertime, and stored for winter use.
- Cheyenne: Leaves mixed with tobacco and used for smoking.
The uses included the making of a root and leaf tea to treat diarrhea, dysentery, and mouth/throat ulcers. The leaves of the plant were smoked for asthma. The blossoms were used by the Chippewa in a mouthwash for teething children. Dye was also created from various parts of the smooth sumac. The fruits were used to make red dyes and the inner bark used to make yellow dyes.
Rhus glabra L. (smooth sumac) has been used in the treatment of bacterial infections like syphilis, gonorrhea, dysentery, and gangrene by North American people.
Archaeological evidence extends the time depth of this use: In 2020, archaeologists unearthed a pipe at a dig in Central Washington state, showing chemical evidence that a Native American tribe had smoked R. glabra either alone or in a blend with tobacco, perhaps "for its medicinal qualities and to improve the flavor of smoke."
2.2 Eclectic and Early American Medical Traditions (19th–Early 20th Century)
King's American Dispensatory (1898), the principal pharmacopeial reference of Eclectic medicine, described the plant's action extensively. Sumach bark was characterized as tonic, astringent, antiseptic, and decidedly alterative; the berries were described as refrigerant and diuretic. In decoction or syrup, the bark of the root was considered valuable in gonorrhoea, leucorrhoea, diarrhoea, dysentery, hectic fever, scrofula, and in profuse perspiration from debility.
Externally, the bark of the root in powder, applied as a poultice to old ulcers, was described as an excellent antiseptic. A decoction was also used as an injection for prolapsus uteri and ani and leucorrhoea, and as a wash in many cutaneous diseases.
Sumach berries were described as astringent and refrigerant. A strong decoction, or the fluidextract diluted, was said to afford a very effective and pleasant gargle in angina, especially in combination with potassium chlorate.
Excrescences produced under the leaves, resembling Chinese galls in character and containing large quantities of tannic and gallic acids, were used as a substitute for imported galls by some American practitioners, who considered them in every respect preferable. They may be collected at little expense, as they were produced very abundantly, especially in the Western States.
3. Key Constituents and Active Compounds
3.1 Tannins
The dominant pharmacologically active class in Rhus glabra is hydrolyzable tannins. Sumach berries have an agreeably acid, slightly styptic taste, which is due, according to W. J. Watson, to malic acid and tannic acids; besides these they contain malate of calcium, gallic acid, fixed and volatile oils, red coloring matter, etc.
The leaves of Rhus glabra, collected in Iowa, contained about 16 percent of tannin. Virginia-grown leaves usually yield 20 to 25 percent. The galls (excrescences) are even richer: Henry Trimble collected galls from the leaves of R. glabra and found they contained 61.70 per cent of tannin, reckoned on the weight of the air-dried galls, or 70.90 per cent of the weight of absolutely dry material.
From the experiments of Stenhouse, it appears that the tannic acid of sumach is identical with that of galls, being, like it, resolved under the influence of sulphuric acid into glucose and gallic acid, and this change is supposed to take place spontaneously in sumach when long kept.
3.2 Phenolic Acids and Other Polyphenols
The antimicrobial activity of the methanol extract and isolated constituents of Rhus glabra was evaluated against 11 microorganisms. The extract was subsequently fractionated, leading to the isolation of three antibacterial compounds: the methyl ester of 3,4,5-trihydroxybenzoic acid (methyl gallate) (MIC 12.5 µg/ml), 4-methoxy-3,5-dihydroxybenzoic acid (MIC 25 µg/ml), and gallic acid (MIC >1000 µg/ml). The first two compounds (methyl gallate and 4-methoxy-3,5-dihydroxybenzoic acid) were reported for the first time from Rhus glabra in that study.
The bark of the root contains albumen, gum, starch, tannic and gallic acids, caoutchouc, soft resin, coloring matter, and probably a volatile odorous principle.
3.3 Organic Acids
W. J. Watson ascertained that free malic acid and acid calcium malate coexist in the berries, which contain also tannic and gallic acids, fixed oil, extractive, red coloring matter, and a little volatile oil. Malic acid is primarily responsible for the characteristically tart, lemon-like flavor of the ripe drupes and explains their historical use as a cooling beverage.
3.4 Flavonoids
Rhus species are notably rich in flavonoids, and their extracts exhibit strong antioxidant and free-radical-scavenging activities. While detailed flavonoid profiling studies specific to R. glabra are limited compared to those for closely related species such as R. coriaria and R. chinensis, the genus-wide pattern of flavonoid accumulation is well-documented. Members of the genus — including Rhus coriaria, Rhus verniciflua, and Rhus chinensis — have been extensively studied and reported to contain diverse bioactive constituents such as flavonoids, polyphenols, and triterpenoids with strong antioxidant and anticancer properties.
3.5 Fixed and Volatile Oils
Oil of Rhus may be extracted from the seeds of this and other species of the genus. It will attain a tallow-like consistency on standing. The volatile oil fraction is minor in quantity but contributes to the aroma profile of the plant, particularly of the leaves and bark.
4. Established Mechanisms of Action
4.1 Astringency and Protein Precipitation (Tannin-Mediated)
The high tannin content of R. glabra — particularly in leaves, bark, and galls — underpins several of the plant's traditional applications. Hydrolyzable tannins and gallic acid interact with proteins in mucous membranes and microbial cell walls, causing precipitation and thereby conferring astringent, antidiarrheal, and topical antiseptic effects. The fluidextract affords an excellent astringent in relaxing diarrheas and other conditions where the tannin drugs are useful.
4.2 Antimicrobial Mechanisms
The antimicrobial activity of the methanol extract and isolated constituents of Rhus glabra (Anacardiaceae) was evaluated against 11 microorganisms, including gram-positive and gram-negative bacteria. Among the isolated antibacterial compounds, methyl gallate demonstrated the strongest activity at MIC 12.5 µg/ml, followed by 4-methoxy-3,5-dihydroxybenzoic acid at MIC 25 µg/ml. These compounds showed better activity against the gram-negative bacteria than against the gram-positive bacterium Staphylococcus aureus.
4.3 Antioxidant Mechanisms
The polyphenolic constituents of R. glabra function as antioxidants through multiple mechanisms including direct free radical scavenging, inhibition of lipid peroxidation, and modulation of mitochondrial membrane dynamics. The DPPH assay demonstrated strong free radical scavenging abilities, with an IC50 value of 18.4 ± 1.4 µL. Mitochondria isolated from rat liver were utilized to examine antioxidative effects on mitochondrial K+ATP ion channels and the mitochondrial permeability transition pore (mPTP). Lipid peroxidation (LPO) was measured via malondialdehyde (MDA) production, indicating that the preparation inhibited LPO and oxidative stress in mitochondrial membranes.
5. Scientific Evidence by Area of Use
5.1 Antimicrobial Activity
Evidence strength: Preliminary — in vitro only.
The primary peer-reviewed study directly examining R. glabra for antimicrobial activity is the 1994 study published in the Journal of Ethnopharmacology. The antimicrobial activity of the methanol extract and isolated constituents of Rhus glabra was evaluated against 11 microorganisms, including gram-positive and gram-negative bacteria. The extract was fractionated and monitored by bioassays leading to the isolation of three antibacterial compounds: methyl gallate (MIC 12.5 µg/ml), 4-methoxy-3,5-dihydroxybenzoic acid (MIC 25 µg/ml), and gallic acid (MIC >1000 µg/ml).
This constitutes purely in vitro evidence. No clinical trials in human populations evaluating R. glabra for infectious disease indications have been identified in the peer-reviewed literature. The study demonstrates mechanistic plausibility for traditional uses related to infection control, but it is unlikely in the view of some commentators to lead directly to new antibacterial drugs.
5.2 Antioxidant and Cardioprotective Activity
Evidence strength: Preliminary — in vitro and animal models only.
A 2024 study published in Plant Science Today (Aripov et al., DOI: 10.14719/pst.3442) is the most direct investigation of antioxidant and cardioprotective properties specific to Rhus glabra. This research examined the heart-healthy and antioxidant effects of a polyphenol mixture made from Rhus glabra using multiple experimental approaches.
- Free radical scavenging: The DPPH assay was used to test the antiradical activity. It showed strong free radical scavenging abilities, with an IC50 value of 18.4 ± 1.4 µL.
- Mitochondrial antioxidant effects: Mitochondria isolated from rat liver were utilized to examine antioxidative effects on mitochondrial K+ATP ion channels and the mitochondrial permeability transition pore (mPTP). Lipid peroxidation was measured via malondialdehyde (MDA) production, indicating that the preparation inhibited LPO and oxidative stress in mitochondrial membranes.
- Cardioprotective effects (animal model): The study employed an adrenaline-induced ischemia model to evaluate cardioprotective effects. Treatment with the polyphenol preparation significantly reduced enzyme markers such as ALT, AST, CK, and LDH compared to the ischemic group, highlighting its potential in mitigating ischemic damage.
- Metabolic indices: Creatine kinase activity assays indicated improved cellular energy metabolism and biochemical profiling revealed enhancements in atherogenic, cardioprotective, and coronary risk indices.
These findings are significant in scope but limited to preclinical (cell-based and rat model) experiments. No randomized controlled trials or human clinical studies investigating R. glabra for cardiovascular outcomes have been identified.
5.3 Anti-inflammatory Activity
Evidence strength: Preliminary — genus-level in vitro and animal data; no human clinical data specific to R. glabra.
A systematic review evaluating anti-inflammatory effects across multiple Rhus species (published via ResearchGate and Academia, assessing 35 studies, following PRISMA guidelines) found that: in vitro studies consistently demonstrated the ability of Rhus plants to reduce key inflammatory mediators such as TNF-α, IL-1β, and IL-6. In vivo studies confirmed these effects in murine models of inflammation, with doses mostly of 400 and 800 mg/kg body weight, with no reports of toxicity. However, the species analyzed in that review were Rhus verniciflua, Rhus chinensis, Rhus coriaria, Rhus succedanea, Rhus tripartita, Rhus crenata, and Rhus trilobata — not R. glabra directly. Fifty-four distinct inflammatory mediators were assessed in vivo; no consistent pattern of mediators was identified that could elucidate the anti-inflammatory mechanisms of the action of Rhus in acute or chronic inflammation. The one clinical trial identified reported anti-inflammatory effects in humans at 1000 mg/kg for 6 weeks — this finding pertains to the broader genus, not specifically to R. glabra.
5.4 Gastrointestinal Uses (Antidiarrheal, Astringent)
Evidence strength: Traditional use well-documented; no modern clinical trials.
The use of R. glabra as an astringent for diarrhea, dysentery, and gastrointestinal irritation is among the most consistently recorded applications across both Native American ethnobotany and the Eclectic medical tradition. The uses included the making of a root and leaf tea to treat diarrhea, dysentery, and mouth/throat ulcers. Sumach bark was described as tonic, astringent, antiseptic, and decidedly alterative; in decoction or syrup, the bark of the root was found valuable in diarrhoea, dysentery, hectic fever, and scrofula.
The mechanistic basis — high tannin content causing mucosal protein precipitation and reduced gut secretion — is chemically plausible and consistent with general tannin pharmacology. However, no randomized controlled trials specific to R. glabra for gastrointestinal endpoints in humans have been identified.
5.5 Urinary Tract Applications
Evidence strength: Traditional use only; no clinical trials identified.
Cherokee tradition records the use of sumac berries for urinary complaints, including red berries chewed for bedwetting. The berries were additionally characterized as refrigerant and diuretic in the Eclectic tradition. No clinical studies evaluating R. glabra for urinary tract indications have been identified in the peer-reviewed literature.
5.6 Topical/Dermatological Uses
Evidence strength: Traditional use only; no clinical trials specific to R. glabra.
Cherokee tradition records the use of an infusion poured over sunburn blisters. Externally, the bark of the root in powder, applied as a poultice to old ulcers, was considered an excellent antiseptic. The astringent and antimicrobial properties of the plant's tannin and phenolic acid content provide a plausible mechanistic basis for topical application, but no controlled human studies exist.
5.7 Respiratory Uses
Evidence strength: Traditional use only; no clinical trials identified.
The leaves of the plant were smoked for asthma in some Native American traditions. The Flathead tribe used an infusion of green or dried branches taken for tuberculosis. These applications are ethnobotanically documented but entirely unsupported by modern clinical evidence.
6. Body Systems and Health Areas of Association
Based on the documented traditional uses and available scientific literature, Rhus glabra has been associated with the following body systems and health areas:
- Gastrointestinal system: Astringent applications for diarrhea, dysentery, mouth/throat ulcers; gargle for tonsillar inflammation.
- Cardiovascular system: Preclinical evidence of antioxidant and cardioprotective effects mediated through mitochondrial pathways.
- Urinary system: Traditional diuretic and urinary soothing uses.
- Integumentary system (skin): Topical antiseptic applications for ulcers, sores, sunburn blisters, and cutaneous eruptions.
- Respiratory system: Traditional use in asthma (smoked leaves) and tuberculosis (infusions).
- Reproductive/gynecological system: Bark infusion traditionally used to stimulate milk flow; decoction used for leucorrhoea.
- Immune/anti-infective: In vitro antibacterial activity against a range of gram-positive and gram-negative bacteria.
7. Dosage Forms and Reported Dosages
Dosage information specific to Rhus glabra is limited to historical pharmacopeial records. No modern clinical trials have established dose-response relationships in humans. The following data are drawn exclusively from documented historical sources:
- Fluidextract (Fluidextractum Rhois Glabrae): The dose of the fluidextract is fifteen to thirty minims (1–2 mils).
- Decoction/infusion of root bark: Used as a gargle and oral preparation in unspecified quantities in the Eclectic tradition; precise doses are not standardized in the available literature.
- Topical powder/poultice: Applied externally as needed in historical practice, with no defined weight-based dosing.
- Polyphenolic extract (experimental/preclinical): The 2024 Plant Science Today study used a polyphenol preparation (designated "PC-5") in cell and rat studies at laboratory quantities; no human dose equivalent is established from this work.
Across the genus-level systematic review of anti-inflammatory studies, in vivo studies employed doses mostly of 400 and 800 mg/kg body weight, but these data pertain to other Rhus species in animal models, not to R. glabra in humans.
8. Safety Considerations
8.1 Distinction from Toxic Rhus Species
Great care is necessary in the selection of the several species of Rhus, as many of them are extremely poisonous. The critical botanical distinction is between Rhus glabra — a non-toxic edible and medicinal species — and members of the former Rhus genus now reclassified as Toxicodendron (poison ivy, poison oak, poison sumac), which contain the potent contact allergen urushiol. The name "rhus" in medical literature comes from the former botanical classification of these toxic plants. While they are now classified as Toxicodendron, the medical term "rhus dermatitis" persists.
Rhus dermatitis (from urushiol-containing species) is an allergic contact dermatitis affecting up to 75% of the population. This Type IV hypersensitivity reaction occurs when urushiol penetrates the skin and binds to proteins, triggering an immune response that causes intense itching, redness, swelling, and characteristic linear blistering patterns. Rhus glabra does not contain urushiol and is not associated with this condition.
8.2 Tannin Load and Gastrointestinal Tolerance
Given the exceptionally high tannin content of R. glabra leaf and bark — approximately 16 percent in Iowa-collected leaves, and 20 to 25 percent in Virginia-grown leaves — high-dose or prolonged oral use carries the theoretical risk of gastrointestinal irritation, nausea, and potential hepatotoxicity that is associated with excessive tannin ingestion generally. However, no specific toxicological studies on R. glabra tannins at human-relevant doses have been identified in the peer-reviewed literature.
8.3 Cross-Sensitivity within the Anacardiaceae Family
Individuals sensitized to members of the Anacardiaceae family (mango, cashew, pistachio, poison ivy) may theoretically exhibit cross-reactivity to other members of the family, including R. glabra. This risk is documented for the family broadly but has not been specifically quantified for R. glabra in controlled studies.
8.4 Pregnancy and Lactation
Although some Native American traditions used R. glabra bark infusions to stimulate milk flow postpartum, the Cherokee used an infusion of bark taken to make human milk flow abundantly — no modern safety evaluation of this use during pregnancy or lactation has been identified in the peer-reviewed literature. The high tannin and gallic acid content raises theoretical concerns that have not been systematically addressed in human studies.
8.5 Potential Drug Interactions
No specific drug interaction studies involving Rhus glabra preparations have been identified in the peer-reviewed literature. Theoretically, gallic acid and tannic acid can chelate minerals and may interfere with the absorption of certain oral medications, consistent with the known behavior of tannin-rich plant preparations generally. No human pharmacokinetic interaction data specific to R. glabra are available.
8.6 Evidence Quality Assessment
The overall body of evidence for Rhus glabra as a medicinal supplement is weak by modern standards. The majority of documented biological activity derives from:
- Historical ethnobotanical records and 19th-century pharmacopeial monographs
- A small number of in vitro antimicrobial studies
- One published preclinical study (2024) evaluating antioxidant and cardioprotective effects in rat liver mitochondria and an adrenaline-induced ischemia model
- Extrapolation from genus-level (Rhus spp.) pharmacological data
No randomized controlled clinical trials evaluating Rhus glabra for any health indication in human populations have been identified in the peer-reviewed literature as of the date of this article. Accordingly, all health claims associated with R. glabra remain either traditionally derived or supported only by preliminary preclinical evidence.
References
Go back