Black Locust (Robinia pseudoacacia L.)
1. Identity, Taxonomy, and Natural Source
Botanical Classification and Nomenclature
Robinia pseudoacacia L., commonly known as black locust, is a medium-sized hardwood deciduous tree belonging to the tribe Robinieae of the legume family (Fabaceae). Another common name is false acacia, a literal translation of the specific name (pseudo meaning fake or false, and acacia referring to the genus of plants with the same name).
The species is also commonly called common locust, yellow locust, white locust, green locust, pea flower locust, and false acacia. The black locust is referred to as "false acacia" after its species name "pseudoacacia," although it is not particularly closely related to the true acacia, which belongs to the mimosa subfamily (Mimosoideae).
The genus name Robinia honors Jean Robin (1550–1629), of Paris, gardener to Henri IV and Louis XIII of France, who received new plants from Canada. The specific epithet pseudoacacia means false acacia.
Geographic Origin and Distribution
Native to the Appalachian and Ozark mountain ranges in the eastern United States, black locust has been widely naturalized across North America and other continents. It is considered native from Pennsylvania through the Appalachians to northern Georgia and westward to Arkansas and Oklahoma. It is documented from every conterminous state in the United States, and also occurs in Ontario to Nova Scotia and British Columbia.
Although fossilized traces of the genus were found in Europe, the species itself is native to a few small areas of the United States but has been widely planted and naturalized elsewhere, including temperate North America, Eurasia, and Africa. It is considered an invasive species in some regions. The tree was introduced to sub-Mediterranean and temperate regions, including continental Europe, Australia, and East Asia, of which China alone possesses over one million ha of plantation. In 2010, the estimated area of R. pseudoacacia plantations outside their native range was about 3 million ha, and the number keeps growing.
Botanical Description
The black locust is a fast-growing, medium-sized deciduous tree known for its fragrant white flowers, nitrogen-fixing abilities, and adaptability to various soil conditions. This tree may reach 25 meters (82 feet) tall and up to 120 centimeters (47 inches) in diameter. The bark on older trees is thick and deeply furrowed. It has an upright, narrow crown, widest at the top, producing masses of white, fragrant pea-like flowers that mature into flat pods in the fall.
Like all species from the Fabaceae family, it fixes nitrogen. The wood is rot resistant, very hard, and durable.
Common Preparations and Forms
The plant parts most relevant to medicinal and dietary use are the flowers, bark, leaves, and seeds, though these differ greatly in their safety profiles (see Safety section). The flowers are white, borne in pendulous racemes of 10–15 cm long, and are edible, with high nutrient and functional values. Common preparation forms reported in traditional and research contexts include:
- Infusions and decoctions made from the flowers, used as gentle remedies for headaches, gastrointestinal discomfort, and mild sedation.
- In European herbal practice, the fragrant flowers were included in teas and herbal blends aimed at soothing digestive disturbances, such as heartburn and mild gastritis, owing to their mild laxative and anti-inflammatory effects.
- Black locust syrup (particularly in the Polesie region of Eastern Europe) is used as an antispasmodic, expectorant, diuretic, choleretic, sedative, hemostatic, antipyretic, laxative, hypotensive, anti-inflammatory, and healing agent.
- Polyphenolic extracts of R. pseudoacacia flowers have been prepared using hydro-ethanolic extraction in research settings.
- Acacia honey is produced by bees pollinating and collecting nectar from the flowers of the black locust tree (Robinia pseudoacacia), also known as the false acacia.
- In laboratory research, compounds have been extracted from leaves and flowers with 70% ethanol and 80% methanol.
2. Traditional and Historical Use
Indigenous North American Use
Native to the eastern United States, black locust was used by Indigenous peoples, such as the Cherokee, for tools, bows, and medicinal purposes, leveraging its durable wood and bark's astringent properties. Native American tribes were among the first to recognize its therapeutic potential, employing various parts of the plant—especially the flowers and bark—for their purported medicinal properties.
The tree was identified in 1607 at Jamestown by British colonists, who used the timber to build houses.
Introduction to Europe and European Traditions
The black locust was first introduced to Europe in the early 1600s. Jean Robin, a botanist serving the French kings Henry III, Henry IV, and Louis XIII, is credited with planting the first black locust seeds in Europe. In 1601, Robin planted the seeds in one of his gardens, marking the beginning of the tree's European journey.
In European herbal practice, the fragrant flowers of Robinia pseudoacacia were praised for their calming and antispasmodic qualities. They were commonly included in teas and herbal blends aimed at soothing digestive disturbances, such as heartburn and mild gastritis, owing to their mild laxative and anti-inflammatory effects. The plant also found its way into cough syrups and respiratory preparations, where its soothing action helped alleviate throat irritation.
The flowers of false acacia are used in traditional medicine as diuretic, spasmolytic, sedative, and cholagogic agents, and to relieve inflammation of the kidneys and biliary ducts.
Eastern European Ethnobotany
Of the two species of the genus Robinia, which are native to North America and introduced in Polesie (a region spanning Ukraine and Belarus), black locust (R. pseudoacacia) is traditionally used as a medicinal, technical, and food plant. In that region, black locust syrup is used as an effective antispasmodic, expectorant, diuretic, choleretic, sedative, hemostatic, antipyretic, laxative, hypotensive, anti-inflammatory, and healing agent. The flowers are also used as an antipyretic, and for the prevention of diseases of the lungs and bronchi, and as an effective antispasmodic for spasms of internal organs or muscles.
Traditional Indian and Asian Use
In traditional medicine of India, different parts of R. pseudoacacia are used as laxative, antispasmodic, and diuretic. The flowers, bark, and leaves of R. pseudoacacia have been used in traditional medicine for antitussive, laxative, and cholagogue purposes.
Food and Honey Production
Black locust is a major honey plant in the eastern United States, and, having been taken and planted in France, is the source of the renowned acacia monofloral honey from France. Acacia honey, derived primarily from the nectar of the black locust tree (Robinia pseudoacacia), is renowned for its light, clear appearance and mild, delicate flavor with subtle floral notes. It has a low glycemic index of around 32–35, lower than the average of approximately 55 for most honeys, due to its high fructose content.
In Liguria, Italy and Romania, the flowers are sometimes used to produce a sweet and perfumed jam. Black locust jam contains vitamin C and other nutrients that help strengthen the immune system, support healthy skin, and improve digestion.
3. Key Constituents and Active Compounds
Overall Phytochemical Profile
The bioactive molecules present in R. pseudoacacia include alkaloids, flavonoids, tannins, phenols, and steroids. Phytochemical screening of different solvent extracts identified alkaloids, flavonoids, saponins, tannins, and phenols; positive results were obtained specifically for flavonoids, tannins, and phenols.
Flavonoids
In the chemical composition of Robinia pseudoacacia L., the literature has cited the presence of the following flavonoids: robinin (kaempferol-3-O-ramnozil-galactozil-7-ramnozid), acacetin-7-O-rutosid, apigenin, diosmetin, luteolin, secundiflorol, mucronulatol, isomucronulatol, and isovestitol.
Five flavonoids—acacetin, secundiflorol I, mucronulatol, isomucronulatol, and isovestitol—were isolated from the ethanolic extract of the whole plant of Robinia pseudoacacia (Fabaceae).
In total, 64 compounds were identified in Croatian specimens, of which flavonols (20) and hydroxycinnamic acid derivatives (15) were the most represented. Flavanols such as catechin dominated in leaf extracts, followed by flavonols, with kaempferol glucuronyl rhamnosyl hexosides as the main compound. Flower extracts had the highest share of flavones, followed by ellagitannins, with luteolin dirhamnosyl hexosides and vescalagin, respectively, being predominant.
Acacetin (the Principal Bioactive Flavone)
Acacetin (5,7-dihydroxy-4′-methoxyflavone), one of the flavones of flavonoids, is a monomethoxy flavonoid that exists in a variety of plants in free form or glycoside form, including Robinia pseudoacacia. Acacetin has been isolated from black locust (Robinia pseudoacacia), bee propolis, Dracocephalum moldavica, Turnera diffusa, and Betula pendula, as evidenced by chemical profiling in peer-reviewed studies.
Acacetin has attracted wide attention from the scientific community because of its various pharmacological activities, including anti-inflammatory, anticancer, anti-obesity, anti-diabetic, neuroprotective, and cardioprotective effects.
Robinin
Important constituents of the plant are the toxalbumin robin, which loses its toxicity when heated, and robinin, a nontoxic glucoside. Robinin has been identified as kaempferol-3-O-rhamnosyl-galactosyl-7-rhamnoside, a flavonoid glycoside found predominantly in the flowers.
Lectins: Robin and Phasin
The species contains the lectins robin and phasin, which are found in the leaves, bark, and seeds. The severity of toxicity largely depends on the degree of mastication of toxin-containing tree parts. These toxalbumins, robin and phasin, exert their toxic effects by inhibition of protein synthesis. The inner bark of black locust contains two different lectins, RPbAI (major lectin) and RPbAII (minor lectin).
Other Phenolic Compounds
Oxidative stress-related activity of extracts can be attributed to rutin, hyperoside, epigallocatechin, ferulic acid, quercetin, and related compounds. Flowers of Robinia pseudoacacia contain high levels of phenolic compounds and minerals that have pronounced antioxidant properties.
4. Established Mechanisms of Action
Antioxidant Activity
Antioxidant capacity, measured by ABTS (17.49–146.41 mg TE/g DW), DPPH (24.67–118.49 mg TE/g DW), and FRAP (7.38–77.53 mg TE/g DW) assays, was higher in leaf than in flower extracts. Antiradical in vitro tests showed that acacia honey was more antioxidant than nectar, which was even able to induce oxidative stress directly in a eukaryotic cell system.
Anti-inflammatory Mechanisms
Research has shown that R. pseudoacacia leaf extract inhibited secretion of SEAP, blocked IL-1β signaling, and inhibited IL-1β–mediated angiogenesis in ex vivo and in vitro assays. The extract inhibited nuclear translocation of NF-κB by suppressing phosphorylation of IL-1β signaling protein kinases and inhibited mRNA expression of IL-1β–induced pro-angiogenic factors including VEGFA, FGF2, ICAM1, CXCL8, and IL6.
Cardiovascular Mechanisms (Acacetin)
The protective effects of acacetin on multiple cardiovascular diseases — including arrhythmias, cardiac ischemia/reperfusion injury, atherosclerosis, myocardial hypertrophy and fibrosis, drug-induced cardiotoxicity, diabetic cardiomyopathy, hypertension, and cardiac senescence — appear to involve suppressing oxidative stress, reducing inflammation, preventing cardiomyocyte apoptosis and endothelial cell injury, as well as regulating mitochondrial autophagy and lipid metabolism.
An acacetin phosphate prodrug applied in ischemia/reperfusion injury experiments showed that acacetin inhibited the apoptosis of myocardial cells by preventing the reduction of antioxidants such as SOD-2 and thioredoxin and reducing the release of inflammatory cytokines such as TLR4, IL-6, and TNFα, thus playing a protective role on the myocardium after myocardial infarction. Further studies confirmed that the antioxidant, anti-inflammatory, and antiapoptotic effects of acacetin on cells are mediated by AMPK-mediated Nrf2 activation.
Apoptosis Induction in Cancer Cells
The flavonoid polyphenolic compound acacetin (5,7-dihydroxy-4′-methoxyflavone) derived from Robinia pseudoacacia showed an anti-proliferation effect in A549 lung cancer cells (IC50 = 9.46 μM). In HepG2 cells, acacetin inhibited cell growth and induced cell cycle arrest at G1 phase and apoptosis through increases in levels of p53 protein and its downstream pro-apoptotic targets, p21/WAF1 and Bax proteins.
Antimicrobial Activity
The aromatic substances and phenolic compounds in flower extracts exhibit antimicrobial properties against foodborne pathogenic bacteria including Salmonella, Escherichia coli, and Listeria monocytogenes. Black locust flower extracts were found to be efficient antibacterials for Gram-positive cocci. The antibacterial potential of extracts and their fractions, as well as some of their natural compounds, has been shown against oral pathogens including E. coli, Streptococcus mutans, and Porphyromonas gingivalis, which cause periodontal inflammatory diseases and dental caries.
Renal Protective Mechanisms
In vitro experiments with NRK52E renal tubular epithelial cells demonstrated that a Ganoderma lucidum and Robinia pseudoacacia flower extract complex (NEPROBIN) significantly alleviates H₂O₂-induced oxidative stress and suppresses lipopolysaccharide (LPS)-induced activation of the MAPK and NF-κB signaling pathways. Additionally, NEPROBIN reduced LPS-induced NF-κB transcriptional activity and downregulated the expression of cytokines and chemokines in these cells.
5. Scientific Evidence by Area of Use
5.1 Oncology / Anticancer
Evidence level: Preclinical only (in vitro and cell-line studies); no human clinical data.
Acacetin isolated from R. pseudoacacia was significantly cytotoxic in the prostate cancer cell line (PC-3), as determined in bioactivity studies against a panel of six solid human tumor cell lines. Acacia honey derived from R. pseudoacacia nectar exhibited effective anticancer activity in a dose-dependent manner against breast (MCF-7), colon (HCT-116), and lung (A549) cancer cell lines, with corresponding IC₅₀ values of 5.053 μg/mL, 5.382 μg/mL, and 6.728 μg/mL, respectively, in an in vitro investigation.
An in vitro study found that R. pseudoacacia leaf extract (RP) inhibited secretion of SEAP, blocked IL-1β signaling, and inhibited IL-1β–mediated angiogenesis in ex vivo and in vitro assays. RP inhibited nuclear translocation of NF-κB by suppressing phosphorylation of IL-1β signaling protein kinases and inhibited mRNA expression of IL-1β–induced pro-angiogenic factors including VEGFA, FGF2, ICAM1, CXCL8, and IL6. The conclusion drawn was that RP suppressed IL-1β–mediated angiogenesis and could be a promising agent in anticancer therapy. These findings are preliminary and derive entirely from laboratory models; no clinical trials in humans have been conducted.
5.2 Cardiovascular System
Evidence level: Preclinical only (animal and cell studies); no human clinical trials identified for R. pseudoacacia extracts per se.
Acacetin, a natural flavonoid derived from various plants including Robinia pseudoacacia, has been demonstrated to have a wide spectrum of pharmacological properties including antioxidant, anti-inflammatory, antibacterial, and anti-tumor activities. Increasing numbers of studies, mostly preclinical, have indicated that acacetin has potential cardiovascular protective effects and might become a novel therapeutic strategy for cardiovascular diseases.
In an animal study, administration of acacetin in ischemia/reperfusion (I/R) rats significantly reduced the arrhythmia score from 4.90 to 2.50 and the reperfusion arrhythmia score from 3.79 to 1.82 in the vehicle or the acacetin group, respectively. In cultured primary cardiomyocytes and H9C2 cells, acacetin reduced hypoxia/reoxygenation-evoked cell injury by blocking oxidative stress, apoptosis, and inflammation via the upregulation of AMPK/Nrf2 signaling.
Acacetin is described as a potent molecule for its anti-inflammatory and anti-cancer activity; however, further scientific evidence is essential to validate its potency in disease models associated with inflammation and cancer. There is limited information available for toxicity profiling of acacetin, and further studies would aid in establishing this natural flavone as a candidate for clinical research.
5.3 Antimicrobial Activity
Evidence level: In vitro only; no clinical trials.
Extracts of R. pseudoacacia leaves and flowers had good quorum sensing, biofilm formation prevention, and eradicating capacity in laboratory studies. The results provided new insights into the phytochemical properties of R. pseudoacacia as a first step toward its potential pharmaceutical use.
In a well-diffusion assay investigating acacia honey, a high mean growth inhibition zone was observed against Staphylococcus aureus (48.33 ± 1.53 mm), Escherichia coli ATCC 10536 (38.33 ± 1.53 mm), and Staphylococcus epidermidis ATCC 12228 (39.33 ± 1.15 mm). The microdilution assay revealed that low concentrations of acacia honey could inhibit the growth of almost all the evaluated bacterial and fungal strains, with minimal bactericidal concentration values (MBCs) ranging from 75 mg/mL to 300 mg/mL. These studies were performed in vitro and do not constitute evidence of clinical efficacy in humans.
5.4 Antioxidant Activity
Evidence level: In vitro; limited in vivo animal data; no randomized controlled human trials.
Antioxidant capacity measured by ABTS, DPPH, and FRAP assays in Croatian specimens was higher in leaf extracts than in flower extracts, with ABTS values reaching up to 146.41 mg TE/g DW in leaf extracts. Characterization by high-performance liquid chromatography–diode array detection of 18 plant molecules demonstrated acacia honey to be richer than R. pseudoacacia nectar in secondary metabolites. All antioxidant measurements to date have been conducted in laboratory assays and their relevance to in vivo human health outcomes has not been established in controlled clinical trials.
5.5 Renal and Anti-fibrotic Effects
Evidence level: In vitro and animal; no human clinical trials.
A combination extract complex of Ganoderma lucidum and Robinia pseudoacacia flowers (NEPROBIN) effectively mitigated an adenine diet (AD)–induced inflammatory response in the kidneys, with a marked reduction in cytokine and chemokine expression. This decrease in inflammation was associated with a significant reduction in tubulointerstitial fibrosis. Overall, NEPROBIN alleviated renal damage and fibrosis by directly targeting renal oxidative stress and inflammation, highlighting its potential as a therapeutic agent for chronic kidney disease. The evidence remains limited to preclinical models, and the contribution of the R. pseudoacacia component independently could not be isolated from the combination product.
5.6 Respiratory Use
Evidence level: Traditional use only; no controlled clinical evidence identified.
In Polesie folk medicine, black locust flowers have been regarded as effective as an antipyretic and for the prevention of diseases of the lungs and bronchi, and as an effective antispasmodic. No peer-reviewed clinical trials evaluating these specific respiratory indications in humans were identified in the literature reviewed.
5.7 Gastrointestinal Use
Evidence level: Traditional use only; no controlled clinical evidence identified.
In European herbal practice, the fragrant flowers of Robinia pseudoacacia were praised for their calming and antispasmodic qualities and were commonly included in teas and herbal blends aimed at soothing digestive disturbances, such as heartburn and mild gastritis, owing to their mild laxative and anti-inflammatory effects. These applications are based on traditional use and have not been validated in human clinical trials.
6. Body Systems and Health Areas
- Cardiovascular system: Acacetin from R. pseudoacacia has been studied preclinically for effects on arrhythmias, cardiac ischemia/reperfusion injury, atherosclerosis, myocardial hypertrophy and fibrosis, drug-induced cardiotoxicity, diabetic cardiomyopathy, hypertension, and cardiac senescence.
- Immune and inflammatory system: The flowers, bark, and leaves have been used in traditional medicine for antitussive, laxative, and cholagogue purposes, effects attributed to the bioactive molecules including alkaloids, flavonoids, tannins, phenols, and steroids.
- Oncology (preclinical): The flavonoid acacetin derived from R. pseudoacacia showed an anti-proliferation effect in A549 cells (IC50 = 9.46 μM), and induced apoptosis and cell cycle arrest via upregulation of p53 and p21/WAF1 proteins at concentrations of 5 or 10 μM.
- Renal system: The flowers are used in traditional medicine as diuretic and cholagogic agents to relieve inflammation of the kidneys and biliary ducts.
- Digestive system: Different parts of R. pseudoacacia are used in traditional Indian medicine as laxative, antispasmodic, and diuretic.
- Antimicrobial: Black locust flower extracts were efficient antibacterials for Gram-positive cocci, and extracts have shown antibacterial potential against oral pathogens including Streptococcus mutans and Porphyromonas gingivalis.
7. Dosage Forms and Dosages Reported in Studies
No standardized or regulatory-approved dosages for R. pseudoacacia extracts as a dietary supplement have been established by any major pharmacopeial authority, including the European Pharmacopoeia, USP, WHO, or Commission E. The following dosage-related information is reported from research contexts only:
- In cell-line studies, acacetin demonstrated anti-proliferative effects in A549 lung cancer cells at an IC50 of 9.46 μM and induced apoptosis and cell cycle arrest at concentrations of 5 or 10 μM.
- Cytotoxicity against the prostate cancer cell line PC-3 was established from an ethanolic whole-plant extract; exact concentrations were determined in bioactivity assays but were not separately stated in accessible abstracts.
- In an in vitro investigation of acacia honey, antioxidant activities were expressed as DPPH-IC50 = 0.670 mg/mL and ABTS-IC50 = 1.056 mg/mL. Minimal inhibitory concentrations for bacterial strains ranged from 75 mg/mL to 300 mg/mL in microdilution assays.
- In an animal (rat) ischemia/reperfusion model, acacetin treatment significantly reduced the arrhythmia score from 4.90 to 2.50 and the reperfusion arrhythmia score from 3.79 to 1.82; precise dosing was documented in the original study but not reported in the accessible abstract.
- In phytochemical screening studies, extraction was performed with 70% ethanol and 80% methanol to characterize the phenolic content of leaves and flowers.
No human clinical dosage recommendations have been derived from these laboratory data. Flower infusions and syrups used in folk traditions have not been subject to dose-finding clinical studies in the peer-reviewed literature reviewed.
8. Safety Considerations and Interactions
Part-Specific Toxicity
The bark, leaves, and wood are toxic to both humans and livestock. Important constituents of the plant are the toxalbumin robin, which loses its toxicity when heated, and robinin, a nontoxic glucoside.
Except from the inflorescences (flower clusters), all parts of the plant are toxic, especially the bark and seeds. The toxic compounds include the glycoside (robitin), the alkaloid (robinin), and lectins (robin, ricin, and phasin).
Mechanism of Toxicity
The Black Locust contains toxalbumins, robin and phasin, that exert their toxic effects by inhibition of protein synthesis. These lectins are structurally similar to other plant toxalbumins and interfere with cellular protein biosynthesis at the ribosomal level.
Clinical Poisoning Cases
Despite the potential dangers of black locust intoxication, reports of human toxicity after ingestion are rare. A reported case represented the first human intoxication of black locust bark in North America in over one hundred years: an eight-year-old male was brought to the emergency department 6 hours after chewing and expelling the black locust bark. He presented with emesis, which began approximately 2.5 hours after exposure.
A case report describes the poisoning of two mares from the same paddock with Robinia pseudoacacia bark. The poisoning manifested by sudden onset of weakness and fever with transient improvement after the administration of non-steroidal anti-inflammatory drugs and fluids. After initial stabilization, one of the mares was found dead in the morning. Necropsy of the dead mare revealed oedema of the brain and lungs, pleural haemorrhages, and hyperaemia and haemorrhages of the glandular mucosa of the stomach.
Horses that consume the plant show signs of anorexia, depression, incontinence, colic, weakness, and cardiac arrhythmia.
Differential Toxicity by Plant Part
The bark, sprouts, leaves, pods, and seeds of the black locust tree are toxic, although various reports suggest that the seeds and the young pods can be edible when cooked, since the poisons contained in this plant are decomposed by heat. Important constituents are the toxalbumin robin, which loses its toxicity when heated, and robinin, a non-toxic glucoside. However, the flowers are generally considered less toxic than the bark, seeds, and leaves, and are the part most commonly referenced in traditional medicinal and food use.
Heat Stability Considerations
The toxalbumin robin loses its toxicity when heated. This characteristic underpins the traditional practice of consuming flowers and, occasionally, cooked seeds in some regions; however, the extent to which heat reliably denatures all toxic fractions across preparation methods has not been systematically established in clinical research.
Acacetin Safety
Acacetin is a potent molecule reported for its strong anti-inflammatory and anti-cancer activity; however, further scientific evidence is essential to validate its potency in disease models. There is limited information available for toxicity profiling of acacetin, and further studies would aid in establishing this natural flavone as a potent candidate for research studies at the clinical level.
Absence of Interaction Data
No peer-reviewed data from controlled studies characterizing pharmacokinetic or pharmacodynamic drug interactions for Robinia pseudoacacia flower preparations or standardized acacetin supplements in humans were identified in the literature reviewed. The lack of such data constitutes a substantive gap in the safety characterization of this ingredient.
Summary of Evidence Strength
The overall body of evidence for Robinia pseudoacacia as a dietary supplement or therapeutic ingredient is preliminary and largely preclinical. Antioxidant, anti-inflammatory, antimicrobial, and anticancer activities have been demonstrated consistently in in vitro and some animal models. The principal bioactive flavone acacetin has been more extensively characterized in cardiovascular preclinical research. Despite these promising findings, robust human clinical trials investigating the nutritional or therapeutic effects of Robinia pseudoacacia are lacking. Traditional use across multiple cultures provides historical context, but does not constitute clinical evidence of efficacy or safety at specific doses.
References
Go back