Black poplar

Black Poplar (Populus nigra L.): A Comprehensive Reference

1. Identity, Taxonomy, and Natural Source

Botanical and Chemical Identity

Populus nigra L. (family Salicaceae) is one of the most widely recognized trees found in deciduous forests. It is commonly known in English as black poplar or European black poplar; in phytotherapy literature the drug material from the buds is referred to by the Latin pharmacopoeial name Populi gemmae. The species epithet nigra, meaning "black," refers to the dark tone of the bark in mature specimens.

The Populus genus includes more than 40 species, being widespread especially in Europe and Asia. Black poplar is a fast-growing deciduous tree species native to Eurasia, with considerable economic value, and acts as a pioneer tree in natural floodplains, contributing to the biodiversity and stability of European ecosystems.

Morphology and Habitat

Black poplar is a tall tree; its height can reach up to 30 m and its diameter up to 2 m. The roots are adherent, and the rhytidome is thick and blackish. The tree thrives in moist, humus-rich soils and is typically found on floodplains, in damp forests, and along riverbanks and other waterways.

The buds — the part of the plant primarily explored in phytotherapy — are large, approximately 2 cm long and 5–8 mm thick, conical, elongated, and yellow-brown, with a sharp, slightly curved tip. Their surface bears viscous resins with a weak balsamic but aromatic smell, and on the central axis there are 4–8 oval and sharp bracts adherent due to the resins, which also give the buds a shiny appearance.

Plant Parts Used and Common Preparations

Many parts of this tree, such as the buds, leaves, and bark, can be used as active ingredients for the pharmaceutical industry. The buds are the most medicinally important part. Poplar buds have been used as tincture, infusion, powder, or ointment. The resinous exudates present on the buds have been the major plant source used by bees to form propolis.

2. Traditional and Historical Use

Ancient and Classical Medicine

The application of salicin-rich bark in medicine significantly predates modern pharmaceutical science. Ancient Greek, Roman, and Middle Eastern civilizations commonly used bark decoctions from willow and poplar to treat symptoms of fever and acute pain. Populus nigra appears in ancient texts dating back to Greek and Roman herbalists; Dioscorides mentioned populi cortex for treating wounds and ulcers.

In the bark of P. tremula (European aspen), Braconnot identified salicin and another crystallizable principle he named populin, and in these compounds the febrifuge properties of the bark likely reside.

Medieval and Early Modern European Medicine

In Europe, poplar buds appeared for the first time in John Gerard's book (1597), which described the use of the buds in a healing ointment with beneficial effects against inflammations. Analysis of historical data indicates that the medicinal use of black poplar was important and diverse in the past, and became focused on the Populeon Ointment after the 16th century.

Unguentum populeum is the oldest formulation prepared from poplar buds, used and continuing to be used for its anti-inflammatory and antihemorrhoidal properties. The tincture was recommended as a remedy in asthma and other respiratory conditions, such as bronchitis, cough, tracheitis, laryngitis, sore throat, influenza, gout, and pulmonary hemorrhage, while the ointment was used in the treatment of dermatological disorders such as ulcerations, hemorrhoids, anal fissures, and in gouty and rheumatic inflammation. The poplar bark was applied topically in superficial skin lesions, sunburns, insect bites, and contusions.

Folk Medicine across Cultures and Regions

In traditional phytotherapy, importance was also given to poplar bark, which was assigned astringent, anti-inflammatory, anti-rheumatic, and antiseptic properties. In Algeria, the traditional uses of P. nigra are broad in the treatment of many conditions related to endothelial dysfunction, inflammation, arthritis, and respiratory infection.

In North America, Native American medicine systems widely incorporated poplar bark, particularly the flexible inner bark (phloem), for its reliable healing properties; tribes prepared strong teas or poultices to address ailments such as rheumatism, muscular aches, and persistent fevers.

Populus nigra L. (Salicaceae) flower buds are traditionally used in the treatment of dermatitis, upper respiratory tract infections, rheumatism, and wounds. In European traditional medicine, black poplar buds were generally recommended as a remedy in respiratory infections (cough, laryngitis, bronchitis, sore throat) and also in the treatment of dermatological problems (psoriasis), rheumatic inflammations, and hemorrhoids.

3. Key Constituents and Active Compounds

Overview of Phytochemical Classes

The vegetal product has been described mainly to contain phenolic compounds (phenols, phenolic acids, and phenylpropanoids), terpenoids (mono- and sesquiterpenoids), flavones (e.g., apigenin and chrysin), flavanones (e.g., pinocembrin and pinostrobin), caffeic/ferulic acids and their derivatives, and more than 48 phytocompounds in the essential oils.

Populus nigra L., belonging to the Salicaceae family, is rich in a wide variety of phytochemicals found in its aerial parts, including chrysin, α-curcumene/ar-curcumene, caffeic acid phenethyl ester, salicin, caffeic acid, chlorogenic acid, p-coumaric acid, ferulic acid, isoquercetin, quercetin, luteolin, kaempferol, apigenin, cinnamic acid, rosmarinic acid, ellagic acid, hemiterpenes, monoterpenes, sesquiterpene hydrocarbons, 1,8-cineole, eugenol, pinostrobin, pinocembrin chalcone, and pinobanksin-3-acetate.

Phenolic Glycosides

Phenolic glycosides such as salicin, salireposide, and benzoylsalicin (populin) are essential compounds of black poplar buds and other Salicaceae family members. In black poplar bark extracts, salicylic acid glycosides, salicortin, salireposide, benzoic acid derivatives, populin (salicin-6-benzoate), and tremulacin (salicin-2-benzoate) have also been identified.

Flavonoids

The resinous exudate of the black poplar buds contains the flavonoid aglycons: the flavanones pinocembrin and pinostrobin; the flavonols galangin, quercetin, and kaempferol; the flavones chrysin and apigenin; and the esters of phenolic acids. Studies have also demonstrated the presence of flavanones (pinocembrin, pinostrobin, pinobanksin, naringenin), additional flavones (tectochrysin, luteolin), flavanonols (taxifolin), and glycosides (myrcitrin, luteolin-7-O-glucoside).

Phenolic Acids and their Derivatives

According to Dudonné et al. (2011), poplar bud extract was mainly composed of phenolic acids (caffeic, p-coumaric, ferulic, isoferulic, di-O-methylcaffeic, and cinnamic acids), followed by salicylates (salicin) and flavonoid aglycons. Identified phenolic compounds also include dihydroxybenzoic acid, protocatechuic acid, 3-caffeoylquinic acid, 5-caffeoylquinic acid, chicoric acid, apigenin-glucuronide, tremuloidin, and tremulacin.

Essential Oil Components and Terpenoids

The essential oil obtained from black poplar buds comprises predominantly sesquiterpenoids (α- and β-eudesmol, γ-selinene, δ- and γ-cadinene, α-elemene, curcumene, bisabolene, farnesol, humulene) and a few monoterpenoids (1,8-cineole). Approximately 50 molecules have been identified in the essential oils of P. nigra buds, and over 100 molecules including phenolic compounds, flavonoids, terpenoids, and flavanones have been found in various aerial parts of the plant.

Geographic Variation in Composition

Greenway et al. tested the chemical composition of Populus nigra L. bud exudates from 7 countries (Netherlands, Russia, Belgium, United Kingdom, France, Italy, and China) and reported that all screened samples contained high levels of caffeic and isoferulic acids but low levels of cinnamic and coumaric acids; only the UK sample showed an increased percentage of pinocembrin, pinobanksin, chrysin, and galangin.

A study by Ristivojević et al. identified more than 75 phenolic compounds in poplar bud ethanolic extracts collected from Serbia, reporting phenolic acids and their derivatives (caffeic acid and p-coumaric acid), flavan-3-ols (four diastereoisomers of catechin), flavonols, flavanonols, glycosides (apigenin-7-O-glucoside), and phenolic glycerides.

Additional Constituents

Poplar bud extracts have been reported to contain volatile oil (sesquiterpenes, sesquiterpenoids, and derivatives of benzoic acid), tannins, resins, gallic acid, and saponins. Phytochemical investigations have also revealed the presence of tannins, triterpene derivatives, wax, α- and β-amirenol, glucose, and fructose.

4. Mechanisms of Action

Anti-inflammatory Mechanisms

The content of salicylates and flavonoids from poplar extracts are mainly responsible for their anti-inflammatory, analgesic, spasmolytic, and antibacterial properties. Black poplar leaf and bud extracts have shown significant inhibition of pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α in vitro.

Studies using a hen's egg chorioallantoic membrane test system examined the anti-inflammatory effect of the willow bark constituents salicin and tremulacin (isolated from Populus spp.); the onset of anti-inflammatory effect is delayed compared with saligenin, sodium salicylate, and acetylsalicylic acid, indicating that the active principles may be metabolites of salicin and tremulacin. Isolated tremulacin, subcutaneously injected at 100 mg/kg body weight, significantly inhibited carrageenan-induced paw edema and peritoneal leucocyte migration in rats, and croton oil-induced ear edema and acetic acid-induced writhing in mice; inhibition of leukotriene B4 biosynthesis in pleural leucocytes also supported anti-inflammatory activity.

Treatment with particular flavanones or extracts from buds of P. nigra decreased the IL-6 and IL-1β release in human gingival fibroblast (HGF-1) cells, with down-regulation of mRNA for both cytokines observed; COX-2 protein expression was demonstrated for pinocembrin.

Anti-inflammatory potential has been illustrated by lipoxygenase and cyclooxygenase inhibition (52.80 ± 0.2% and 53.88 ± 2.55%, respectively).

Antioxidant Mechanisms

Analysis has revealed predominantly polyphenolic compounds, including phenolic acids and flavonoids — secondary metabolites recognized for their antioxidant properties, particularly valuable in alleviating oxidative stress disorders. Treatment with Populus nigra ointment upregulated the antioxidant marker enzymes catalase and superoxide dismutase activities in granulation tissues.

Hypouricemic Mechanism

Studies have investigated the effect of black poplar bud extract on xanthine oxidase (XO) activity in vitro and its hypouricemic action. The hypouricemic effect of P. nigra bud ethanolic extract was studied in normal mice; after administration of the extract at doses of 100, 200, and 400 mg/kg, a significant decrease (p < 0.01) of uric acid level by 38–43% was recorded.

Vasorelaxant Mechanism

Vasorelaxant effects were estimated in endothelium-intact and endothelium-rubbed rings of porcine coronary arteries; the results showed moderate antioxidant activity (40%) but potent anti-inflammatory activity (49.9%) on carrageenan-induced mice paw edema, and complete protection against AlCl₃-induced hepatic toxicity as revealed by histopathologic examination.

5. Scientific Evidence by Area of Use

5.1 Anti-inflammatory and Analgesic Activity

The most extensively studied property of Populus nigra extracts is anti-inflammatory activity. The available evidence is predominantly preclinical (in vitro and animal models), with no published randomized controlled trials in humans specific to this species identified in the peer-reviewed literature.

Antioxidant and anti-inflammatory activities were assessed using the ABTS test and the animal model of carrageenan-induced paw edema; results showed moderate antioxidant activity (40%) but potent anti-inflammatory activity (49.9%) on carrageenan-induced mice paw edema.

An in vitro study evaluated and compared the anti-inflammatory activity of leaf-bud extracts from Populus nigra, P. × berolinensis, and P. lasiocarpa and the flavanones pinocembrin and pinostrobin in human gingival fibroblasts pro-inflammatorily stimulated by silver nanoparticles; the extracts were standardized on pinocembrin and pinostrobin content. Treatment with P. nigra extracts decreased IL-6 and IL-1β release in HGF-1 cells, with down-regulation of mRNA for both cytokines observed. The potential protective role of pinocembrin and pinostrobin and extracts from buds of P. nigra against AgNPs-induced inflammation and cytotoxicity in HGF-1 cells was demonstrated. These results are limited to a cell-culture model.

Evidence strength: Preliminary; confined to in vitro and animal models. No human clinical trials have been identified for this species specifically.

5.2 Wound Healing

One study assessed the wound healing potential of black poplar ointment containing 10% or 20% of Populus nigra ethanolic flower bud extract. Two ointments (10% and 20%) were prepared from Populus nigra flower buds ethanolic extract and topically applied on the area of excised skin of the rats for either 14 or 20 days, with morphological, macroscopic, histological, and biochemical parameters evaluated. The extract was found to contain high amounts of total phenols (89.5 ± 7.7 mg caffeic acid equivalent/g of extract) and hydrolysable tannins. Treatment with Populus nigra ointment (10% and 20%) promoted wound contraction of 97.37 ± 1.19% and 97.28 ± 0.91%, respectively.

Evidence strength: Preclinical only (rat excision model). Results are promising but not yet confirmed in human trials.

5.3 Antimicrobial Activity

Populus nigra bud extract and exudates have demonstrated good antimicrobial activity against Gram-positive bacteria including Staphylococcus aureus, Streptococcus pyogenes, Listeria monocytogenes, L. innocua, L. welshimeri, and L. seeligeri, and activity against Candida strains, attributed to synergism between flavonoids, hydroxyacids, and sesquiterpenes. Additionally, P. nigra bud extract showed antifungal activity against Candida albicans and a moderate activity against Aspergillus niger and Fusarium polyferatum.

Poplar bud extract shows significant inhibitory activity against Gram-positive bacteria in laboratory testing.

Evidence strength: Preclinical (in vitro) only. All antimicrobial findings are from laboratory assays; no clinical studies in humans have been identified.

5.4 Antitumor and Anticancer Activity

Populus nigra extract has been tested in vitro on lung cancer A549, NCI-H292, and breast cancer MCF-7 cell lines, which indicated anticancer activity.

One study evaluated the antioxidant potential, antimicrobial activity, the in vitro anticancer effect (tested on MCF-7 breast cancer cell line), as well as the antiangiogenic and immunomodulatory potential of Populus nigra L. bud extract collected from western Romania. Results showed a dose-dependent decrease of MCF-7 tumor cell viability with an IC₅₀ of 66.26 μg/mL while not affecting healthy cells; phenomena of early apoptotic events at the maximum concentration tested (150 μg/mL) were detected by Annexin V-PI double staining; the extract induced G0/G1 phase cell cycle arrest; and it showed antiangiogenic potential on the chorioallantoic membrane.

The study concluded that poplar bud extract elicited antioxidant activity, antitumor properties on the breast cancer cell line, followed by an antiangiogenic effect and an immunomodulatory potential on human primary dendritic cells.

Evidence strength: Entirely preclinical (cell lines and chorioallantoic membrane model). No human trials exist. These findings cannot be extrapolated to clinical efficacy.

5.5 Hypouricemic Activity (Gout/Hyperuricemia)

Studies have investigated the effect of black poplar bud extract on xanthine oxidase activity in vitro and its hypouricemic action; poplar has been traditionally used in gout- and arthritis-treatment practices in medieval Europe.

One study examined the hypouricemic action of a P. nigra extract (200 mg/kg) by measuring uric acid levels and liver xanthine oxidoreductase activity in normal and hyperuricemic mice; co-administration with AlCl₃ and D-galactose over four weeks restored all test parameters and pyramidal cells in the cerebral cortex, and the extract elicited a significantly hypouricemic effect comparable to that of allopurinol when administered orally to oxonate-induced hyperuricemic mice.

Evidence strength: Animal studies only. The comparison to allopurinol is promising but requires validation in controlled human trials.

5.6 Hepatoprotective Activity

Protection from hepatic toxicity caused by aluminum was examined by histopathologic analysis of liver sections; results revealed complete protection against AlCl₃-induced hepatic toxicity. These results are from an animal model using histopathology, and no human hepatoprotective clinical trials have been identified.

Evidence strength: Animal/preclinical only.

5.7 Antidiabetic Activity

Owing to its phytochemical constituents, P. nigra demonstrates antidiabetic activity among other pharmacological properties. A growing number of studies have reported activity in the development of pharmacological effects related to diabetes and cardiovascular diseases. However, available data are from in vitro and animal models. No human clinical trials on the antidiabetic effects of P. nigra specifically have been identified in the peer-reviewed literature.

Evidence strength: Preliminary; in vitro and animal data only.

5.8 Cardiovascular and Vasorelaxant Activity

Vasorelaxant effect was estimated in endothelium-intact and endothelium-rubbed rings of porcine coronary arteries precontracted with high concentrations of U46619; relaxant effects of the extract on vascular preparation were considerable at 10⁻¹ g/L.

Evidence strength: Ex vivo (porcine tissue) only. No human cardiovascular clinical trials identified.

5.9 Antioxidant Activity

Polyphenolic content in black poplar buds has been measured, ranging from 19.26 to 33.37 mg GAE/g DW and flavonoid content from 2.15 to 4.45 mg RE/g DW. Populus nigra L. bud extract presents an important antioxidant activity due to the rich phytochemical composition. These findings are all from laboratory assays (DPPH, FRAP, ABTS) and have not been tested in clinical trials.

Evidence strength: In vitro assay data only.

5.10 Skin Aging and Dermatological Applications

Black poplar buds are employed for anti-inflammatory, antipyretic, antiallergic, antimicrobial, antidiabetic, and antitumoral properties, and have positive effects on skin infections and antiaging potential. Research into the transcriptional effects on skin aging at the cellular level has been conducted in laboratory models, but no controlled clinical trials in human subjects have been identified.

Evidence strength: Preliminary in vitro data; insufficient for clinical conclusions.

6. Body Systems and Health Areas

• Musculoskeletal system: Black poplar has many traditional uses due to its analgesic–antipyretic, anti-inflammatory, diuretic, astringent, and cicatrizing action. This includes rheumatism, arthritis, gout, and sciatica.
• Respiratory system: The tincture was recommended as a remedy in asthma and other respiratory conditions, such as bronchitis, cough, tracheitis, laryngitis, sore throat, influenza, and pulmonary hemorrhage.
• Integumentary system (skin and wound healing): The ointment was used in the treatment of dermatological disorders such as ulcerations, hemorrhoids, anal fissures, and in gouty and rheumatic inflammation.
• Urinary system: P. nigra buds are recommended for kidney and bladder diseases.
• Hepatic system: Hepatoprotective properties have been demonstrated in animal models as described above.
• Cardiovascular system: Vasorelaxant properties have been demonstrated in ex vivo porcine models.
• Metabolic/uric acid: Poplars have been traditionally used in gout- and arthritis-treatment practices; modern studies confirm xanthine oxidase-inhibitory and hypouricemic properties.
• Immune system: Immunomodulatory potential on human primary dendritic cells has been demonstrated in laboratory research.

7. Dosage Forms and Dosages Reported in Studies

No standardized therapeutic dosages have been established for Populus nigra based on human clinical trials. The following reflects dosage information as it appears in the scientific and traditional literature:

• Experimental ointments (wound healing, rat model): Ointments containing 10% and 20% of Populus nigra ethanolic flower bud extract were applied topically for 14 or 20 days in the rat excision model.
• Ethanolic extract (anti-inflammatory, animal model): Anti-inflammatory activity was assessed using the animal model of carrageenan-induced paw edema, showing potent anti-inflammatory activity (49.9%).
• Hypouricemic dose (animal model): Administration of ethanolic bud extract at doses of 100, 200, and 400 mg/kg resulted in a significant decrease (p < 0.01) of uric acid levels by 38–43% in normal mice.
• Neuroprotective/hypouricemic (animal model): P. nigra extract was co-administered at 200 mg/kg in mice over four weeks.
• In vitro anticancer: A dose-dependent decrease of MCF-7 tumor cell viability was found with an IC₅₀ of 66.26 μg/mL; early apoptotic events were detected at the maximum concentration tested (150 μg/mL).
• Traditional preparations: Poplar buds have been used as tincture, infusion, powder, or ointment in traditional practice. Historical sources for the bark describe doses of bark powder 1–3 grams and bark in decoction 3–9 grams, though these figures derive from traditional (non-clinical) sources.

8. Safety Considerations and Interactions

Salicylate Content and Allergy Risk

Populus nigra contains salicylates, which are similar to the active ingredient in aspirin; it can therefore cause allergic reactions in individuals sensitive to aspirin. Individuals with known salicylate hypersensitivity should treat black poplar products with the same caution applicable to willow bark (Salix spp.) and related Salicaceae preparations.

Gastrointestinal Effects

Black poplar may cause stomach upset or irritation in some people. This is consistent with the general profile of salicylate-containing herbal preparations.

Propolis Cross-reactivity

The resinous exudates present on black poplar buds have been the major plant source used by bees to form propolis. Individuals with known propolis allergy may therefore experience cross-reactive responses to black poplar bud preparations, as propolis derives substantially from Populus nigra resin.

Potential Drug Interactions

Because black poplar contains salicin and related phenolic glycosides, theoretical interactions exist with anticoagulant medications (e.g., warfarin) by additive salicylate effects, consistent with the class-level interaction profile of salicylate-containing botanicals recognized in established herbal pharmacopeia. No specific drug–herb interaction studies for Populus nigra itself have been identified in regulatory monographs reviewed.

Pollen Allergy

Poplar trees are known producers of airborne pollen and are recognized allergens. Individuals with established poplar pollen allergy may potentially exhibit cross-reactivity to botanical preparations derived from the same species, though specific data on cross-reactivity between pollen and bud/bark preparations are limited.

Pregnancy and Lactation

No safety data specific to Populus nigra preparations in pregnancy or lactation have been identified in the peer-reviewed literature or in formal regulatory monographs covering this species. Given its salicylate content, caution is warranted by analogy to the class.

Evidence Limitations and Overall Assessment

Modern scientific validation for black poplar's medicinal benefits is emerging, though comprehensive clinical studies remain limited. Several studies have depicted antioxidant, anti-inflammatory, antibacterial, antifungal, antidiabetic, antitumor, hepatoprotective, hypouricemic properties, and effects on melanin production; all these lead to the conclusion that black poplar buds are a valuable and important source of bioactive compounds responsible for a wide range of therapeutic uses, being a promising candidate as a complementary and/or alternative source for a large number of health problems. Nevertheless, essentially all current evidence is derived from in vitro cell assays and animal experiments. No peer-reviewed randomized controlled trials in human subjects specifically investigating Populus nigra as a dietary supplement or herbal medicine have been identified.

References

• Kis B. et al. (2020). Recent Advances Regarding the Phytochemical and Therapeutic Uses of Populus nigra L. Buds. Plants, 9(11), 1464. PMC7693997.
• Dinu M. et al. (2023). Chemical Composition, Antioxidant Activity, and Antibacterial Activity of Black Poplar Buds' Hydroalcoholic Macerates from Dobrogea Area. PMC10343426.
• Polyphenolic Composition, Antioxidant Activity, and Cytotoxic Effect of Male Floral Buds from Three Populus Species Growing in the South of Romania. PMC11857894.
• Wound healing potential of a formula based on Populus nigra L. flower buds extract with anti-inflammatory activity. PubMed 38729538.
• Kis B. et al. (2022). Antimicrobial activity, in vitro anticancer effect (MCF-7 breast cancer cell line), antiangiogenic and immunomodulatory potentials of Populus nigra L. buds extract. BMC Complementary Medicine and Therapies. PMC8928639.
• Debbache-Benaida N. et al. (2013). Pharmacological potential of Populus nigra extract as antioxidant, anti-inflammatory, cardiovascular and hepatoprotective agent. Asian Pacific Journal of Tropical Biomedicine.
• Tebbi S.O. & Debbache-Benaida N. (2022). Phytochemistry, chemical composition and therapeutic uses of Populus nigra L. aerial parts from 1991–2021 onwards: An overview. Sustainable Chemistry and Pharmacy, 30, 100880.
• Kis B. et al. (2020). Recent Advances Regarding the Phytochemical and Therapeutic Uses of Populus nigra L. Buds. Plants (MDPI open access).
• Inorganic Element Determination of Romanian Populus nigra L. Buds Extract and In Vitro Antiproliferative and Pro-Apoptotic Evaluation on A549 Human Lung Cancer Cell Line. Pharmaceutics (MDPI).
• Pobłocka-Olech L. et al. (2019). Anti-inflammatory and antioxidative effects of the buds from different species of Populus in human gingival fibroblast cells: Role of bioflavanones. PubMed 30668329.
• Anti-hyperuricemic and neuroprotective effects of Populus nigra. Journal of Pharmacy & Pharmacognosy Research.
• Xanthine oxidase inhibitory potential and hypouricemic activity of Populus nigra buds. Planta Medica.
• European Medicines Agency (EMA). Final Assessment Report: Salix various species — Cortex (includes data on Populus-derived tremulacin and salicin).
• Chemical composition and ecological adaptation of Populus (Salicaceae) species and hybrids depending on soil and environmental conditions. RSC Advances, 2026.
• Salicylate metabolism in Populus. PMC3239876.
• Antioxidant and Anti-Inflammatory Potential of Populus nigra L. Buds. Drugs and Drug Candidates (MDPI).