Black Poplar - Populus nigra

Detailed Description

A multifaceted tree with an ancient history.

Botanical Information

The crown of the Black Poplar is broad, tall, and arching, sometimes appearing irregular in older specimens. It is classified as a fast-growing tree. The trunk is usually straight but may become twisted in aged trees. The wood is light brown, coarse, and generally lightweight. The bark ranges from grayish-white to gray-brown, often fissured. Branches are broad, and older twigs often have a yellow-gray hue.

The leaves are borne on long branches, up to 9 cm in length, arranged alternately, with petioles, and range in shape from rounded to long-pointed with finely serrated edges. All leaves are glabrous, light green above and lighter beneath.

Flowers are dioecious—male flowers are thick, cylindrical catkins up to 5 cm long, while female catkins are generally slender, greenish, with yellow stigmas. Black Poplar blooms from March to April. The fruit is a thick, pointed, greenish-brown, glabrous capsule. Seeds are light brown and dispersed by the wind, usually appearing in June.

Origin and Distribution

Black Poplar originates from riparian zones in Central and Southern Europe, though its natural range now stretches from the Mediterranean to the British Isles in the north, and eastward through Western and Central Asia to Kazakhstan and China. The tree is also prevalent in the Caucasus and the Middle East.

Usage / Dosage

Black Poplar is commonly used in avenues and large parks as an ornamental tree and windbreak. It remains one of the most widespread deciduous trees in woodlands. Notably, many parts of the tree serve as sources for pharmaceutical extracts of active compounds.

The species name "Populus" comes from the Latin word for "people." In antiquity, poplars were planted around sites of public gatherings, explaining the historical basis for the tree’s name. In Europe, the medicinal use of poplar buds was first officially recorded in John Gerard’s book (1597) for their inclusion in healing and anti-inflammatory ointments.

Traditional Medicine

In traditional herbal medicine, Black Poplar bark has been valued for its astringent, anti-inflammatory, anti-rheumatic, and antiseptic properties. The tree buds are widely utilized as tincture, infusion, powder, or ointment. Tinctures are recommended for respiratory issues such as asthma, bronchitis, coughs, tracheitis, laryngitis, sore throats, tonsillitis, gout attacks, pulmonary bleeding, and their ointments are used in dermatology for ulcers, surface skin lesions, sunburn, insect bites, bruises, hemorrhoids, anal fissures, and rheumatic inflammation.

Hepatoprotective Properties

Research by Debbache-Benaida et al. demonstrated the hepatoprotective effect of ethanol extract from Black Poplar buds in vivo at 200 mg/kg against aluminum-induced liver toxicity. Histopathological analysis revealed preserved liver architecture, suggesting protection against damage and necrosis.

Antioxidant Effects

Debbache et al. described the in vitro antioxidant activity of poplar bud extracts, showing that aqueous extracts had the highest antioxidant capacity. Both in vitro (RAW 264.7 murine macrophage cells) and in vivo (male mouse model) analysis of ethanol extract revealed potent free radical scavenging activities at various concentrations (10–150 μg/ml in vitro; 25 and 100 mg/kg in vivo).

Another study confirmed strong antioxidant activity in poplar buds using the DPPH test, with ethanol extract showing comparable effect to ascorbic acid (vitamin C) at certain concentrations.

Anti-inflammatory Properties

In addition to robust antioxidant effects, poplar buds are known for their anti-inflammatory properties, largely attributed to the presence of flavonoids such as quercetin, pinocembrin, and phenolic acids.

Dudonne et al. evaluated poplar bud extracts in vitro, finding strong modulation of gene transcription related to inflammatory responses (CCL5) and cell renewal (KLF10, E2F-4, ZFP36L1). Additional research highlighted wound healing and analgesic potential. Ethanol extracts, due to flavonoids (mainly pinocembrin and pinostrobin), significantly reduced pro-inflammatory interleukins IL-6 and IL1β in HGF-1 cell lines.

Further anti-inflammatory potential was evaluated in a mouse model of carrageenan-induced edema at 200 mg/kg, with results comparable to 50 mg/kg diclofenac. Other studies showed that extract concentrations of 25 and 100 mg/kg had significant anti-inflammatory effects by inhibiting cytokines (IL-6, IL-10, TNF-α).

Pinocembrin demonstrated both in vitro and in vivo protection against induced inflammation and regulated interleukins (IL-6, IL-10, IL-1β, TNF-α). In vivo, in acute lung injury models, 20 or 50 mg/kg pinocembrin reduced lung edema and severity at tissue level. Analytical studies found betulin, α-, β-, and γ-betulenol, δ-humulene, and α-caryophyllene as high redox-potential compounds beneficial for skin issues, improving tissue tone, regeneration, and epidermal rejuvenation. Poplar extract presents a promising candidate for future skincare formulations.

Antibacterial and Antifungal Effects

Phenolic compounds provide antibacterial effects. Gulhan Vardar-Unlu et al. detailed methanolic poplar bud extract to be most effective against Gram-positive bacteria such as Staphylococcus aureus, Streptococcus pyogenes, and Enterococcus faecalis.

Further studies showed ethanol extracts from poplar buds act significantly against Pseudomonas aeruginosa and inhibit biofilm formation. Ethanol extracts displayed strong antioxidant activity due to high polyphenol content, and demonstrated in vitro antibacterial activity against Staphylococcus aureus and Listeria monocytogenes. Merghache et al. showed aqueous extract triggers notable antifungal activity against Candida albicans.

An Algerian study reported mild antifungal action against Aspergillus niger and Fusarium polyferatum. Another study suggested that poplar bud extract’s antimicrobial and anti-biofilm properties are linked to apigenin, pinocembrin, kaempferol, and other flavonoids and phenolic acids. Other findings reported marked antimicrobial effects of 100 μl poplar bud extract against Staphylococcus aureus and Bacillus subtilis.

Recently, its efficacy in treating Lyme disease has begun to be explored.

Antidiabetic Properties

In an extensive study, Shiquin Peng et al. evaluated antidiabetic effects of ethanol poplar bud extract. The extract increased insulin sensitivity, decreased insulin resistance, reduced glycated hemoglobin, and glycosylated serum proteins in vivo in diabetic mice. After 4 weeks of 50 or 100 mg/kg/day extract, there was over 25% reduction in serum insulin, with more prominent results than metformin. The extract also reduced inflammatory markers (IL-6, TNF-α, MCP-1, COX-2).

Liu et al. examined in vitro effects of pinocembrin, galangin, chrysin, and pinobanksin on insulin resistance, finding galangin (80 μM) and pinocembrin (4 μM) increased glucose uptake and glycogen content, and their combined effects improved insulin resistance.

Antitumor Properties

While few studies examine antitumor potential of Black Poplar extract specifically, active compounds, especially pinocembrin, show broad pharmacological effects—antimicrobial, anti-inflammatory, neuroprotective, antioxidant, and in regulating reactive oxygen species and apoptosis.

In human prostate cancer cell lines, 100–150 μM pinocembrin displayed antiproliferative and pro-apoptotic properties. Other studies showed pinocembrin’s cytotoxicity against human colon cancer cells. Gao et al. tested concentrations (100–200 μM) in vitro on human ovarian carcinoma, demonstrating effective inhibition of proliferation, migration, and promotion of apoptosis. Pinocembrin at 50, 100, and 200 μM induced apoptosis in human colon cancer cell lines.

Another study found antitumor effects of pinocembrin against melanoma cells in vitro and in vivo; 50–75 mg/kg reduced tumor volume and weight in mice. Pinostrobin also demonstrated anticancer potential; Bail et al. showed antiproliferative effects against breast cancer cells, and other studies describe pinostrobin’s pro-apoptotic potential (in vitro) on cervical cancer cells and its ability to induce apoptosis in breast cancer cell lines at 10, 50, and 100 mg/ml concentrations.

Precautions

Due to the salicylate content of poplar, avoid concurrent use of salicylates. Co-administration with NSAIDs may increase gastrointestinal and renal toxicity. Additionally, combining salicylates with anticoagulants may raise bleeding risk.

Active Compounds

The main compounds in Populus nigra—primarily in the buds—are phenolic compounds (phenols, phenolic acids, phenylpropanoids, and various flavonoids), and terpenoids (mono- and sesquiterpenoids). Large quantities of flavonoids and phenolics are responsible for most biological and pharmacological properties of poplar buds.

The scientific literature notes that Black Poplar buds contain flavones (such as apigenin, chrysin, pinostrobin, pinocembrin, galangin), flavanones (such as pinocembrin and pinostrombin), anthocyanins, saponins, quinones, sesquiterpenes (γ-selinene, elemene, β- and α-eudesmol), flavonols, flavanols, glycosides, and glycerides. Significant phenolic acids also present include caffeic, coumaric, cinnamic, and ferulic acids and derivatives. More than 48 essential oils are identified, such as cadinene, cineole, curcumin, bisabolene, farnesol, humulene, and acetophenone in notable concentrations.

Other identified compounds are 1,8-cineole, salicylaldehyde, cinnamate, ferulic acid, caffeic acid, pinocembrin, p-coumaric acid, and benzyl caffeate.

Traditional Dosage

Pour 200 ml of cold water over one teaspoon of dried Black Poplar buds and bring to a boil. Simmer gently for 10 minutes, strain, and allow to cool to a drinkable temperature. Use twice daily. Poplar buds are also used to make tinctures.