Black-eyed susan

Black-Eyed Susan (Rudbeckia hirta L.): A Comprehensive Reference

1. Identity, Taxonomy, and Botanical Description

Botanical name: Rudbeckia hirta L. Family: Asteraceae (formerly Compositae). Carl Linnaeus named the genus Rudbeckia in honor of Olaf Rudbeck the son, who was a botanist and professor at Uppsala University and whose father founded Sweden's first botanical garden. The species epithet hirta refers to the plant's hairy leaves and stems.

Common names: The plant is botanically named Rudbeckia hirta and goes by a range of common names including coneflower, brown-eyed Susan, blackiehead, yellow daisy, golden Jerusalem, brown Betty, gloriosa daisy, poorland daisy, yellow ox-eye daisy, and hairy coneflower.

Geographic origin and distribution: Rudbeckia hirta is native to Eastern and Central North America, including ten Canadian provinces and all 48 contiguous states. The plant is native to Eastern and Central North America and has since been naturalized in Western North America and in China.

Botanical description: Black-eyed Susan is an upright flowering plant that can be either biennial or perennial depending on the climate, belonging to the sunflower (coneflower) family Asteraceae. It is an upright annual (sometimes biennial or perennial) plant with alternate, mostly basal leaves 10–18 cm long, covered by coarse hair, with stout branching stems and daisy-like, composite flower heads appearing in late summer and early autumn. It grows 30–100 cm (12–39 in) tall by 30–45 cm (12–18 in) wide. Its blooming season begins in June and continues all summer until September.

Parts used medicinally: The plant's roots, leaves, and flowers have been used to make tea and various extracts, as well as poultices and ointments. Notably, the seeds are considered potentially poisonous and are not recommended for consumption.

Common preparation forms: Roots, leaves, and flowers can be used to make teas, decoctions, extracts, poultices, and washes. Flowers and leaves should be harvested in the morning when in peak bloom, and roots should be harvested after the plant has produced seeds by digging deep to obtain the entire taproot; plant materials may be used fresh or dried for later use.

2. Relationship to Echinacea and the Broader Rudbeckia Genus

The genus Rudbeckia contains more than 20 species, of which R. hirta, R. fulgida, R. laciniata, R. maxima, R. occidentalis, and R. triloba are best known for their decorative value. It shares a close botanical kinship with Echinacea, a well-known herbal remedy, and boasts similar medicinal properties. It has a long history of traditional use for its anti-inflammatory and antimicrobial properties, which have been confirmed through a number of scientific studies. Investigation into bioactive compounds has revealed that Rudbeckia spp. also exhibit antioxidant, anti-tumor, immunomodulating, and antimycobacterial properties.

3. Traditional and Historical Use

3.1 Native American Traditions

Indigenous people across North America have used Rudbeckia for food and medicine, as well as in applications related to spirituality and goods such as perfume. The most common use of Rudbeckia is as a snakebite or earache remedy. Records of traditional uses of Rudbeckia range from treating colds and fevers to application as an abortifacient.

R. hirta is most commonly used as an external wash for snakebites, but it is also used to treat colds, diarrhea, earaches, gonorrhea, headaches, indigestion, sores, and sunstroke.

Specific tribal uses, documented in the ethnobotanical literature, include the following:

• Ojibwa (Chippewa): The Ojibwa people used the plant as a poultice for snake bites and to make an infusion for treating colds and worms in children.
• Cherokee and Iroquois: The Cherokee and Iroquois tribes used the plant as an anthelmintic (to expel parasitic worms), especially in the form of infusions prepared from the roots. Cherokee tribes also used coneflowers to relieve the discomfort of many gynecological and venereal issues.
• Potawatomi: The Potawatomi Indians made tea from the roots, which was believed to have immunostimulating properties that relieve symptoms of the common cold.
• Menominee and Potawatomi: The plant has diuretic properties and was used by the Native American tribes Menominee and Potawatomi to increase the flow of urine.
• Root juice for earaches: A juice extracted from the roots has been used to treat an earache.
• Gynecological and venereal applications: Various root extracts have also been used to treat gynecological conditions and sexually transmitted diseases.

There have been records of different Native American tribes using the plant to aid in the treatment of dropsy, worms, snakebites, and earaches.

3.2 Adoption by European Settlers

Upon arriving in North America, early European settlers quickly adopted the knowledge of Native Americans regarding black-eyed Susan's medicinal uses and incorporated it into their own herbal traditions, further solidifying its role in early American herbalism.

3.3 Overview of Preparation Methods in Traditional Use

• Root tea/decoction: The roots of black-eyed Susan were commonly brewed into teas or decoctions to stimulate the immune system, and native people often used them to treat symptoms of colds, flus, and infections.
• Root infusion for internal use: In some Native American herbal medicines, an infusion of the black-eyed Susan roots was used to treat colds, dropsy, and worms in children.
• Poultice (external): A poultice made from the plant was often applied externally to treat minor wounds, sores, and snake bites.
• Root juice (for earaches): A juice made with the root of this plant was used to treat earaches.
• Tincture: The tincture has been used as a substitute for Echinacea angustifolia.

4. Key Phytochemical Constituents

Untargeted metabolite profiling and UHPLC-HR-MS phytochemical analysis revealed the presence of more than 250 compounds in R. hirta pertaining to different classes, including sesquiterpene lactones, polyphenolic acids, flavonoids, amino acids, and fatty acids.

4.1 Sesquiterpene Lactones

Bioactive sesquiterpene lactones, such as rudmollin, rudmollitrin, alloalantolactone, 3-oxoalloalantone, and rudbeckolide, as well as chlorogenic acids, flavanol glycosides, phenolic acids, and polysaccharides, are abundant in many Rudbeckia species.

Sesquiterpenes representing the Asteraceae family — i.e., germacrene D, δ-cadinene, and a pseudoguaianolide-type lactone, rudbeckolide — which showed potent 5-LOX inhibitory activity in vitro, were isolated from the flowers of R. hirta.

Pseudoguaianolide-type sesquiterpene lactones such as rudbeckin A, rudbeckolide, rudmollin, and acetoxyrudmollin have been previously isolated from the genus Rudbeckia. Minor lactones 4-acetoxyrudmollin, 15-acetoxyrudmollin, and rudmollitrin were also obtained; rudmollin and 15-acetoxyrudmollin exhibited activity in the P-388 lymphoid leukemia system.

4.2 Flavonoids and Polyphenolic Acids

Flavonoids identified in R. hirta include quercetin and its glycosides, kaempferol, and others including eupatolin, patuletin, and derivatives of quercetagetin, which have antibacterial, anti-inflammatory, and antioxidant properties. The plant is also known to contain polyphenolic acids, including caffeic and chlorogenic acids.

Secondary metabolites found in extracts include polyphenols and flavonoids such as caffeic, chlorogenic, and gentisic acids, patuletin, quercetin, quercetagetin, and quercetagitrin.

4.3 Polyacetylenic and Polyinic Compounds

The inflorescences and roots of the species also contain several classes of polyacetylenic and polyinic compounds, such as thiophenes, thiarubrines, and tridecapentaynenes, with implications for the insecticidal properties observed in different extracts obtained from the plant.

4.4 Polysaccharides

Recent research on black-eyed Susan has been primarily concerned with the polysaccharides and aqueous ethanol extracts of the root of the plant. Experimentation determining the value of the antioxidant properties of the polysaccharides in the root has examined their ability to inhibit peroxidation of soybean lecithin liposomes by OH radicals.

An arabinogalactan-protein from Rudbeckia hirta L. enhances the secretion of granulocyte-macrophage colony-stimulating factor and activates the complement system in the classical and alternative ways; the immunomodulatory effect is dose-dependent.

4.5 Terpenes and Other Constituents

Terpenes in R. hirta are thought to be responsible for the plant's distinctive taste and smell and its antibacterial properties. The most well-represented categories of compounds according to chromatographic analysis were sesquiterpene lactones, flavonoid O-glycosides, amino acids and derivatives, quinic acid derivatives, and coumaric acid derivatives.

5. Established Mechanisms of Action

5.1 Lipoxygenase (LOX) Inhibition — Anti-inflammatory Mechanism

The compound rudbeckolide exhibited strong 5-lipoxygenase inhibitory activity (84.9% inhibition at 10 μg/mL) in vitro, and this result provided partial scientific evidence for the usage of the plant as a traditional medicine. The in vitro 5-LOX inhibitory, immunomodulatory, and antioxidant (oxygen radical absorbance capacity) activities of isolated compounds were evaluated, and the results provided new scientific evidence for the ethnopharmacological use of the herb in inflammatory conditions.

5.2 NF-κB Pathway Modulation

A recent study found that the R. hirta methanolic extract (RHME) exhibits a multi-target protective effect against colitis through modulation of NF-κB and CXCL10/CXCR3 inflammatory pathways, alongside maintaining redox hemostatic balance.

5.3 Antioxidant Mechanisms

The flower extract demonstrated potent antioxidant properties through iron chelation and 15-LOX inhibition capacities. The studied compounds were found to be present in most analyzed samples in variable quantities, with the highest quantities found in the ethanolic plant extracts; positive dose-related values revealed that the investigated extracts exhibit good antioxidant activity through multiple investigated mechanisms, including ferric reducing capacity and superoxide radical scavenging.

5.4 Antimicrobial Mechanism

Gram-positive bacteria appear to be more susceptible to the effects of sesquiterpene lactones than Gram-negative bacteria, suggesting that the observed antimicrobial activity may be correlated with the presence of such compounds.

5.5 Immunomodulatory Mechanism

The arabinogalactan-protein from R. hirta enhances the secretion of granulocyte-macrophage colony-stimulating factor and activates the complement system in both the classical and alternative pathways, with the immunomodulatory effect being dose-dependent.

6. Scientific Evidence by Area of Activity

Critical caveat: While preclinical studies indicate that extracts of Rudbeckia hirta may contain bioactive compounds such as flavonoids and phenolic acids with antioxidant and antimicrobial effects, scientific validation in the form of rigorous clinical trials remains limited. Considering that the species is generally associated with its ornamental role, very few studies have focused on the investigation of the secondary metabolites found in the plant and their possible therapeutic use. All current evidence is preclinical (in vitro or animal) unless otherwise stated. No robust human clinical trials on R. hirta as a medicinal supplement have been identified in the peer-reviewed literature.

6.1 Antimicrobial Activity

Evidence level: In vitro only — preliminary.

The untargeted metabolite profiling and UHPLC-HR-MS phytochemical analysis of the extract obtained from R. hirta flowers revealed the presence of over 250 compounds. The investigated extract presented inhibitory activity against Staphylococcus aureus and promising antifungal activity. This 2023 study (published in Plants, PMC10420942) used a methanolic extract of cultivated R. hirta flowers and assessed activity against Gram-positive bacteria. There has also been substantial research dedicated to characterizing the phytochemical constituents and their corresponding bioactivity across Rudbeckia species, particularly the antimicrobial and immunomodulating potential of sesquiterpene lactones and flavanol glycosides. Antifungal activity was noted specifically against Candida parapsilosis in earlier studies cited in the same body of literature. These findings are preliminary and in vitro only.

6.2 Antioxidant Activity

Evidence level: In vitro only — preliminary.

The tested extract exhibited inhibitory activity against Gram-positive bacteria and showed promising antifungal activity. It also demonstrated potent antioxidant properties through iron chelation and 15-LOX inhibition capacities. Polysaccharide fractions from the root have been specifically examined for antioxidant effects: experimentation determined the ability of polysaccharides from the root to inhibit peroxidation of soybean lecithin liposomes by OH radicals. All antioxidant data are currently from in vitro systems; no human trials have assessed antioxidant capacity from R. hirta supplementation.

6.3 Anti-inflammatory Activity

Evidence level: In vitro and animal model — preliminary.

Rudbeckia hirta has been traditionally utilized in Native American medicine for the management of inflammatory conditions and digestive ailments, and a recent study investigated the protective potential of the R. hirta aerial parts methanolic extract (RHME) against colitis in rats, with comprehensive phytochemical analyses. Colitis was induced in rats via intrarectal administration of 4% acetic acid on day 7, and RHME at doses of 100 and 200 mg/kg, or sulfasalazine at 100 mg/kg, was orally administered for 7 consecutive days. The findings suggest that RHME exerts significant anti-colitic activity in a rat model of acetic acid-induced colitis, likely through preservation of mucosal integrity, suppression of inflammatory damage, and restoration of colonic histoarchitecture; oral administration of RHME at 200 mg/kg demonstrated efficacy comparable to the reference drug sulfasalazine. Despite the broad traditional use and reported antioxidant and anti-inflammatory properties of R. hirta, no previous studies had investigated its potential protective effects against colitis before this work. This evidence is from an animal model only and should not be extrapolated directly to human use.

6.4 Immunomodulatory Activity

Evidence level: In vitro and preclinical — preliminary.

Investigation into bioactive compounds has revealed that Rudbeckia spp. also exhibit antioxidant, anti-tumor, immunomodulating, and antimycobacterial properties. The arabinogalactan-protein fraction, in particular, has been shown to activate complement pathways and stimulate granulocyte-macrophage colony-stimulating factor secretion in cellular models. Some laboratory studies suggest that these compounds can inhibit the growth of certain bacteria and reduce oxidative stress, supporting the plant's traditional uses. No human immunomodulatory trials have been published.

6.5 Anticancer / Cytotoxic Activity

Evidence level: In vitro only — very preliminary.

The assessment of cytotoxic activity indicated that the R. hirta flower extract may possess anticancer effects by preventing cell growth under experimental conditions, especially on the MCF-7 cell line. The MCF-7 cell line has functional estrogen and EGF receptors, is dependent on estrogen and EGF for proliferation, and represents a model of early-stage, non-invasive breast cancer; the results showed a higher degree of inhibition on the MCF-7 cell line, indicating a promising anticancer activity of the extract at higher concentrations, with the percentage of inhibition being dose-dependent. Concentrations tested included 10, 25, and 50 µg/mL of Rudbeckia hirta extract applied to MCF-7 human breast cancer cells. Activity against the more aggressive MDA-MB-231 cell line was less pronounced. Importantly, earlier phytochemical work noted that rudmollin and 15-acetoxyrudmollin exhibited activity in the P-388 lymphoid leukemia system. All anticancer evidence is strictly in vitro; the relevance to human cancer therapy is entirely unknown.

6.6 Anthelmintic and Antiparasitic Activity

Evidence level: Ethnobotanical records only — no peer-reviewed experimental data identified.

The Cherokee and Iroquois tribes used the plant as an anthelmintic, especially in the form of infusions prepared from the roots. This traditional use has been consistently documented across multiple tribal records but has not been subjected to controlled scientific investigation.

6.7 Diuretic Activity

Evidence level: Traditional/ethnobotanical — limited preclinical data.

Both R. hirta and the related R. laciniata are described as simple diuretics with feeble cardiac stimulation. Both the tea and tincture can be relied upon to stimulate urine by volume of water but not the solids. These observations are drawn from herbalist literature rather than controlled clinical trials.

6.8 Insecticidal Activity

Evidence level: Laboratory and animal safety data — not directly applicable to human health use.

The insecticidal properties of Rudbeckia hirta have been acknowledged, yet they remain underexplored. A 2025 study aimed to optimize extraction conditions, analyze chemical constituents of ethanol extracts from R. hirta, and assess the insecticidal activity of the extract against Malacosoma neustria testacea larvae. Safety assessments in that study indicated that R. hirta extract exhibited no toxicity to Danio rerio (zebrafish), suggesting potential as a natural alternative to chemical pesticides.

7. Body Systems and Health Areas Associated with R. hirta

• Immune system: Immunostimulant and immunomodulatory activity via polysaccharides and flavonoids; traditional use parallels that of Echinacea.
• Integumentary system (skin): Poultices were used externally to treat minor wounds, sores, and snake bites.
• Respiratory system: A root infusion was used as a warm tea to treat common colds, respiratory infections, and even whooping cough.
• Gastrointestinal system: Traditional use for worms, diarrhea, and indigestion; recent animal research explored anti-colitic effects.
• Urinary system: The plant was traditionally used as a diuretic, supporting kidney and urinary tract health.
• Reproductive/gynecological system: R. hirta has been recorded to have a number of medicinal properties, including dermatological and gynecological applications. Several Rudbeckia species have a long history as dermatological and gynecological aids, especially in the treatment of venereal disease.
• Sensory (ear): Root juice preparations used for earache.
• Oncology (preclinical only): In vitro cytotoxic activity against breast cancer cell lines.

8. Dosage Forms and Doses Reported in the Literature

No standardized commercial dosage regimens have been established for R. hirta supplements by any regulatory body. The following dosage information is drawn exclusively from the sources reviewed:

• Root tea (traditional herbalist guidance): For the tea, use the above-ground plant material strained through cloth to remove the hairs; for dosage, use a teaspoon of the dried plant, taking 1 to 2 teaspoons of the prepared tea up to 3 times a day.
• Tincture (traditional herbalist guidance, referring to the related R. laciniata): For the tincture, use 1 part root to 2 parts alcohol at a rate of 30–40 drops up to 4 times a day. This dosage is cited in relation to the lance-leaf coneflower but is applied by some herbalists to R. hirta as well.
• Methanolic extract in animal study (anti-colitis): RHME was orally administered at 100 and 200 mg/kg for 7 consecutive days in a rat colitis model. These are experimental animal doses with no validated human equivalent.
• In vitro cytotoxic testing concentrations: MCF-7 human breast cancer cells were exposed to different concentrations of Rudbeckia hirta extract at 10, 25, and 50 µg/mL, respectively. These are in vitro concentrations, not clinical doses.

9. Safety, Toxicology, and Interactions

9.1 Skin Irritation

The hairs of the black-eyed Susan can cause irritation to the skin when people come into contact with the plant; the symptoms from skin contact can range from redness and itchiness to blistering and hives. The plant is documented as a skin irritant.

9.2 Respiratory and Allergic Reactions

Although the black-eyed Susan has not been known to poison humans, it should not be eaten; it can cause allergic skin reactions and asthma attacks in people sensitive to the plant. The black-eyed Susan has been reported to be the cause of asthma for people with preexisting lung conditions or allergies.

9.3 Asteraceae Family Cross-Reactivity

The Asteraceae representatives consist of diverse secondary metabolites that exhibit various effects in humans; in particular, sesquiterpene lactones (SLs) may cause sensitization resulting in skin irritation and inflammation. The Asteraceae-related allergy symptoms involve eczema, hay fever, asthma, or even anaphylaxis; there is also evidence of severe cross-reactivity with food and pollen allergens in patients sensitive to Asteraceae allergens. Individuals with known sensitivities to related Asteraceae plants — such as chrysanthemum, ragweed, chamomile, or Echinacea — may be at elevated risk.

9.4 Ingestion and Toxicity

Currently, there is no evidence that the flowers can poison humans when swallowed, but they have been known to poison grazing animals; black-eyed Susans have a disagreeable taste, which could discourage large ingestions. The seeds are potentially poisonous and are not recommended for consumption.

9.5 Autoimmune Conditions

Use of black-eyed Susan should be undertaken with caution in individuals with autoimmune disease, given the plant's reported immunostimulant properties — a concern common to all immunostimulating botanicals in that population.

9.6 Pregnancy

Lance-leaf coneflower (R. laciniata) should not be taken when pregnant, and probably black-eyed Susan (R. hirta) as well, given ethnobotanical records suggesting potential use as an abortifacient within some traditional contexts.

9.7 Animal Toxicity

Rudbeckia hirta is noted as toxic to cats. Conflicting information abounds regarding the precise nature and extent of this toxicity to cats.

9.8 Evidence Gaps and Research Limitations

While there have been some studies into the bioactivity of Rudbeckia spp. extracts and isolated compounds, there is still a large gap between compounds isolated from Rudbeckia and those tested for bioactivity. The discovery of a wide range of biosubstances, together with the biological activity observed for the studied extract in preliminary in vitro studies, paves the way for future investigation of the potential application of the plant in the pharmaceutical and nutraceutical sectors. Despite the promising bioactive profile and historical usage of black-eyed Susan, more comprehensive clinical research is needed to fully confirm its efficacy and safety in human populations. No regulatory body — including the NIH Office of Dietary Supplements, WHO, ESCOP, German Commission E, or the European Pharmacopoeia — has published a formal monograph for R. hirta as a dietary supplement, and it is not currently listed on the NIH National Center for Complementary and Integrative Health (NCCIH) herb database as a primary subject of clinical review.

References

• Preliminary Phytochemical and Biological Evaluation of Rudbeckia hirta Flowers — PMC / MDPI Plants (2023)
• Preliminary Phytochemical and Biological Evaluation of Rudbeckia hirta Flowers — PubMed abstract
• The genus Rudbeckia: A critical review of its traditional medicinal uses, phytochemistry, and pharmacology — Vardeman, Lyles & Quave, Journal of Herbal Medicine (2022); ScienceDirect
• Metabolomics Profiling and Anti-Colitic Activity of Rudbeckia hirta Aerial Parts: Inhibition of NF-κB, Cytokine Storm, and Chemokine-Mediated Immune Cell Recruitment — ScienceDirect (2025/2026)
• Evidence-based medicinal value of Rudbeckia hirta L. flowers — Michael et al., Natural Product Research (2014); ResearchGate
• Chemical Composition and Pharmacological Potential of Rudbeckia hirta L. Review — ResearchGate (2019)
• Asteraceae species as potential environmental factors of allergy — PMC (2019)
• Allergic reactions to the black-eyed Susan flower — Poison Control (poison.org)
• Rudbeckia — ScienceDirect Topics overview
• Rudbeckia fulgida, hirta, and laciniata — The Medicinal Plant Garden, University of Birmingham
• Potentially Harmful Perennials — University of Vermont Extension
• Asteraceae Dermatitis: Everyday Plants With Allergenic Potential — MDedge / The Hospitalist
• Black-Eyed Susan (Rudbeckia hirta) — UIC Heritage Garden, University of Illinois at Chicago
• Rudbeckia hirta — Wikipedia (citing Moerman, D. Native American Ethnobotany, Timber Press, 1998)