Sundew

Sundew (Drosera spp.): A Comprehensive Reference

1. Identity and Botanical Classification

Common name: Sundew. Pharmacopoeial drug name: Droserae Herba.

Drosera is the second largest genus of carnivorous plants, including over 200 species. Typical of the genus are the small, tentacle-like outgrowths of the leaves, which are covered with adhesive glands used to catch and digest insects; the plant uses insects as a source of nitrogen, making it ideally adapted for life in nutrient-poor areas such as peatlands.

The species most relevant to medicinal use are:

• Drosera rotundifolia L. — round-leaved sundew; the principal European species historically used in phytotherapy and homeopathy.
• Drosera intermedia Hayne — oblong-leaved sundew; a European species.
• Drosera anglica Huds. — English sundew; also used in Europe.
• Drosera ramentacea Burch. — a South African/Malagasy species now widely employed in commercial preparations as a substitute for threatened European species.
• Drosera madagascariensis — used in some African traditional medicine systems and increasingly in research.
• Drosera peltata Smith — shield sundew; used in Ayurvedic and Asian traditional systems.

These carnivorous plants have their primary origins in East Africa and Madagascar but are cultivated throughout the world. The main species originally used in cough preparations in Germany, D. rotundifolia, D. intermedia, and D. anglica, are now rarely used due to threat of extinction; instead, D. ramentacea and other Drosera species from Australia are employed.

Sundews are distributed worldwide, from North America, through Europe and Africa, to Asia.

Taxonomic family: Droseraceae. The genus belongs to the order Nepenthales.

Common synonyms and alternative names used in commerce and literature include: Dew Plant, Drosera, Droséra à Feuilles Rondes, Drosera longifolia, Round-Leafed Sundew, Youthwort, Red Rot, Lustwort, Rocío del Sol, Rossolis d'Angleterre.

1.1 Common Forms and Preparations

Droserae Herba generally comprises dried aerial parts of Drosera plants and is usually applied as aqueous or ethanol extract in therapy. The drug Droserae Herba, which is traditionally produced from the dried aerial parts of the plant, is accepted in various pharmacopeias of the world.

Documented preparation forms include:

• Herbal tea (infusion): The average daily dose of Drosera herba is 3.0 g and is mostly used in the form of tea infusions or solid dosage forms. Sundew herb is available in pharmacies as a loose product. To make a tea, boiling water is poured over the herb and left to infuse for ten minutes.
• Tincture: Tinctures prepared with D. rotundifolia leaves may also be used for the treatment of various respiratory diseases.
• Fluid/liquid extract: Used in commercial phytopharmaceutical preparations, particularly in Europe.
• Homeopathic preparations: The tincture is prepared from the active, fresh plant. Homeopathic dilutions (e.g., 6c, 30c) are widely used.
• Dried herb in solid dosage forms (tablets, capsules) marketed in European pharmacies.

2. Traditional and Historical Use

Species of the carnivorous genus Drosera L. have long been a source of valuable natural products. The various phytochemicals characteristic of these species, particularly 1,4-naphthoquinones and flavonoids, have contributed to the diverse utilization of sundews in traditional medicine systems worldwide.

Ancient botanical treatises and pharmacopoeias attribute various properties to the sundew, or Drosera, whose red droplets of mucilage do not dry out in the sun. Certain extracts serve as treatment for corns, verrucas, and burns. Infusions and other extracts are used against coughs, respiratory disorders, tuberculosis, arteriosclerosis, inflammations, intestinal illnesses, and syphilis. These preparations are described as diuretic, soothing and aphrodisiac.

2.1 European Tradition

European sundew species (Drosera rotundifolia L., Drosera intermedia Hayne, and Drosera anglica Huds) have been used as traditional medicines in the therapy of respiratory tract infections. Drosera Herba, comprised chiefly of Drosera rotundifolia, has been commonly used for its spasmolytic properties in the treatment of convulsive or whooping cough since the seventeenth century.

The plant was used empirically by physicians in the sixteenth century (Dodoens), principally outwardly against skin eruptions. It was subsequently introduced into homeopathic Materia Medica by Hahnemann, who proved it with others.

The sundew was historically used in aphrodisiac and love potions in Europe, based on the insects that were lured in and unable to escape its grasp. In the Norse saga the Prose Edda, the "dewdrops" on the leaf tentacles are said to be the tears shed by the goddess Freyja as a result of separation from her husband Óðr. A yellow dye was also made in the Scottish Highlands using round-leafed sundews.

Tea made from sundew flowers and roots was used in traditional medicines in Europe as a treatment for respiratory diseases such as bronchitis and asthma.

Sundew has been used for centuries to treat spasmodic and chesty coughs. Internally, it was used as supportive treatment for whooping cough, dry cough, and to strengthen the heart, as an aphrodisiac; externally it was applied for poorly healing wounds, sunburn, and freckles.

Drosera was pointed out by Hahnemann as the principal remedy for whooping cough. It was recommended by German physicians of the eighteenth century as a panacea for hoarseness, chest disorders, and even for tuberculosis.

Drosera sp. extracts have been mentioned in the literature since the sixteenth century as an important antitussive for different respiratory diseases, including tuberculosis.

2.2 African and Malagasy Traditions

In addition to the round-leaved sundew, the parent plants of Droserae Herba include the Moroccan sundew, the long-leaved sundew, the medium sundew (Drosera ramentacea), and Drosera intermedia. Drosera madagascariensis is particularly suitable as a cough tea. South African species have extensive documented use in local folk medicine for respiratory infections and wound healing.

2.3 Asian Traditions

A German monograph from 1870 praises the spasmolytic and antitussive properties of sundew, with the tincture listed in the German Arzneibuch of 1890 for whooping cough. In Ayurveda, Drosera peltata was integrated into Unani and Siddha systems, labeled as "Sundari" in some regional scripts. Early 20th-century Indian scholars documented its use as an adjuvant in decoctions for bronchitis, combining it with licorice and ginger.

2.4 Pharmacopoeial Recognition

Over time, Drosera moved from folk remedy status toward official pharmacopeias: the British Herbal Pharmacopoeia (1970) lists it under "Droserae herba" for its antitussive action, while the German Commission E monograph approves Drosera extracts for spasmodic cough. Sundew is used for irritable and whooping cough according to Commission E. The drug is also commonly used to treat superficial wounds that heal poorly.

3. Key Constituents and Active Compounds

Drosera species contain physiologically active compounds such as flavonoids, ellagic acid, and naphthoquinones. The relative proportions of these compound classes vary significantly among species and growing conditions.

3.1 Naphthoquinones

The genus Drosera contains naphthoquinones considered as the main constituents involved in activity. Distribution of the two major naphthoquinones, plumbagin and 7-methyljuglone, indicates that almost all different species contain one or other of these quinones.

Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) is a plant-derived quinoid component from the genera of Drosera and Plumbago zeylanica, which possesses various biological activities such as anti-tumor and anti-inflammation, with an alleviative effect on oxidative stress.

Droserone, 3-chloroplumbagin, plumbagin, and its isomer ramentaceone are the most prevalent naphthoquinones synthesized in tissues of plants of the Droseraceae family.

The composition of naphthoquinones differs among Drosera species: D. rotundifolia contains mainly 7-methyljuglone, whereas plumbagin is found in D. intermedia. Plumbagin, known for its antimicrobial properties, is present in relatively large amounts in several species, including D. peltata.

Additionally, Drosera rotundifolia contains 1,4-naphthoquinone derivatives including ramentaceone, ramentone, and biramentaceone. The phytochemistry of the plant also reveals the presence of droserone in roots, hydroxydroserone, and rossoliside.

3.2 Flavonoids

The phytochemical composition of D. rotundifolia is well characterized and consists of a complex mix of flavonoids, mainly flavonols and their glycosides, such as quercetin, isoquercitrin, hyperoside, and 2″-O-galloylhyperoside.

Ethanol extracts of Drosera species contain high concentrations of flavonoids (hyperoside, isoquercitrin, quercetin, and myricetin-3-O-galactoside) together with phenolic acids (ellagic acid). Traces of naphthoquinones are also found in some preparations.

In D. rotundifolia and D. anglica, 2″-O-galloylhyperoside, myricetin-3-O-β-glucopyranoside, and kaempferol-3-O-(2″-O-galloyl)-β-galactopyranoside have been identified for the very first time in this genus.

3.3 Other Constituents

Drosera rotundifolia is also rich in additional chemical compounds including flavonoids such as kaempferol, myricetin, quercetin, and hyperoside; quinones including plumbagin, hydroplumbagin glucoside, and rossoliside; and other constituents such as carotenoids, plant acids, resins, tannins, and ascorbic acid (vitamin C).

D. madagascariensis contains only about one-tenth of the flavonoids and ellagic acid derivatives and only one-percent of naphthoquinones compared to European sundew species like D. rotundifolia and D. intermedia. It appears that not every sundew species is equally suitable as a source for pharmaceutical use.

4. Mechanisms of Action

4.1 Antispasmodic / Bronchospasmolytic Effects

In guinea-pig ileum, extracts of D. rotundifolia led to an antispasmodic effect, possibly by affecting an allosteric binding site of the muscarinic M3 receptors.

An ethanol–water extract, as well as an aqueous fraction of this extract, exerted antispasmodic properties against acetylcholine-induced contractions in ex vivo airway smooth muscle preparations. Contractions induced by 60 mM K+ were also abrogated by the aqueous fraction. Effects on airway smooth muscle could be attributed to the flavonoids quercetin, 2″-O-galloylhyperoside, and hyperoside.

The Drosera extract and aqueous fraction also increased the ciliary beat frequency (CBF) of murine tracheal slices. Quercetin and 2″-O-galloylhyperoside were identified as active compounds involved in the elevation of CBF; both compounds inhibited PDE1A and PDE4D.

Flavonoids have been shown to affect cholinergic M3 and histamine H1 receptors, which leads to a reduction in histamine-induced contractions in bronchial asthma.

4.2 Anti-inflammatory Effects

In investigations of the anti-inflammatory and spasmolytic effects of Drosera rotundifolia, both aqueous and ethanolic extracts inhibited human neutrophil elastase, achieving IC50 values of 5 and 1 µg/mL respectively. The very low naphthoquinone concentrations in the extracts appear not to be responsible for the effect; rather, flavonoids like hyperoside, quercetin, and isoquercitrin, detected in considerable concentrations, may contribute to the activity.

Extracts of D. rotundifolia and D. madagascariensis and their natural compounds (quercetin, isoquercitrin, and hyperoside) turned out to be inhibitors of neutrophil elastase. In addition, extracts of these species and their flavonoids were potent anti-inflammatory agents in a HET-CAM (hen's egg test chorioallantoic membrane) assay, and fractions of D. rotundifolia and D. tokaiensis were reported to suppress the activation of human mast cells.

4.3 Antimicrobial Mechanisms

The antimicrobial activity of extracts of aerial parts of Drosera peltata against oral bacteria was investigated using agar diffusion and dilution micromethods. The chloroformic extract, active against all bacteria tested, showed the most significant antimicrobial properties, with plumbagin, isolated from the extract, identified as the active principle.

Results show that naphthoquinones appear to act via central regulatory proteins such as OmpR and alter the stress response, while flavonoids likely affect biofilm formation by creating an iron-poor environment through iron complexation and additionally influencing polyamine balance, reducing intracellular spermidine levels. Further investigations including assays for iron complexation and analysis of polyamines confirmed the proteomic data.

4.4 Gene Expression Modulation

The biological functions of D. rotundifolia were explored in vitro following treatment of bronchial epithelial cells — potential targets of the pharmacological effects of the herbal medicine. The whole plant ethanolic extract was 1000-fold diluted in water and added to a 16HBE human cell line culture for 3 h or 6 h, with effects on gene expression investigated by RNA sequencing. The mechanisms of action recognized so far are linked to the known effects of specific components, such as flavonoids, but are not completely understood.

5. Scientific Evidence by Area of Use

5.1 Respiratory Conditions: Cough, Bronchitis, and Whooping Cough

The respiratory system is the most extensively studied area of application for sundew. The body of evidence ranges from in vitro and ex vivo pharmacological studies to limited clinical and observational human data.

In vitro and ex vivo evidence:

Extracts from Drosera rotundifolia are traditionally used to treat cough symptoms during a common cold. A study aimed to investigate the impact of extracts from D. rotundifolia and active compounds on the respiratory tract using tracheal slices of C57BL/6N mice ex vivo to examine effects on airway smooth muscle and ciliary beat frequency. Phosphodiesterase (PDE) inhibition assays were carried out to test whether PDE1 or PDE4 are targeted by the active compounds.

Quercetin was confirmed to reduce the in vitro activity of PDE1A and PDE4D. The compounds 2″-O-galloylhyperoside and hyperoside, not previously described as PDE inhibitors, turned out to inhibit PDE4D with IC50 values in the low µM range. 2″-O-galloylhyperoside was also shown to be very effective on PDE1A.

One 2022 study showed for the first time that a Drosera extract and its flavonoid compounds increase the ciliary beat frequency of murine airways, while antispasmodic effects were transferred to airway smooth muscle.

Human cell line evidence:

A 2021 study published in Scientific Reports (Arruda-Silva et al.) examined the effect of a very low dose preparation of D. rotundifolia on the 16HBE human bronchial epithelial cell line. The whole plant ethanolic extract was 1000-fold diluted in water (D. rotundifolia 3×) and added to a 16HBE human cell line culture for 3 h or 6 h, with effects on gene expression investigated by RNA sequencing. This study, while informative about gene expression targets, used an in vitro cell model rather than human clinical subjects, limiting direct clinical inference.

Clinical / human evidence:

The efficacy of homeopathic Drosera-containing remedies for the relief of symptoms or the improvement of quality of life was analysed in clinical studies, which reported positive results. However, the available human evidence is substantially limited by study design.

A case series (Chung, 2018, published in Alternative Therapies in Health and Medicine) studied homeopathic Drosera in whooping cough. The study investigated benefits of homeopathic medicines for whooping cough; it was a case series conducted at one of the suburban hospital clinics of the Ann & Robert H. Lurie Children's Hospital of Chicago. Participants were 20 patients aged 21 months to 20 years. The representative patients all received a 30c dilution of homeopathic pertussinum and a 6c dilution of homeopathic Drosera 3 times daily; the same doses were most often used for the other participants. Outcome measures were verbal feedback from patients or family obtained at follow-up visits. The intensity and duration of participants' coughs were alleviated within days to one week in most cases. This was an uncontrolled case series relying on subjective feedback, with no placebo arm and no blinding, and the homeopathic dilutions used contained no measurable quantity of the parent extract. The results cannot be used to attribute efficacy to Drosera per se.

Many botanical treatments for pertussis have been approved by the German Commission E and it has been proposed that these should be studied in clinical trials to determine if they provide effective symptom relief. Herbs of interest include thyme, sundew (Drosera rotundifolia), English ivy, and others.

Overall evidence strength: The pharmacological rationale for antispasmodic and anti-inflammatory effects is well-supported at the in vitro and ex vivo level. Verified randomized controlled clinical trial evidence for sundew alone as a phytopharmaceutical in respiratory conditions is lacking. The German Commission E positive monograph for cough reflects the historical tradition and available pharmacological data rather than large-scale controlled clinical trials.

5.2 Antimicrobial and Antibiofilm Activity

Whole plant extracts of Drosera rotundifolia and Drosera intermedia proved to be more effective than commercial products and single compounds in biofilm inhibition activity against Escherichia coli strains. Sundew extracts may serve as a potential therapeutic approach for targeting biofilm production.

The bioactive compounds of sundew — flavonoids and naphthoquinones — show biofilm-inhibiting properties against multidrug-resistant, ESBL-producing E. coli strains and open up new therapeutic possibilities.

Safety evaluations through cytotoxicity tests in 3D cell cultures and the Galleria mellonella in vivo model confirmed the safety of the extracts used in these antimicrobial studies.

Antibacterial activity against oral bacteria was reported for extracts of D. peltata, identifying plumbagin as the active component.

A review of plumbagin's antimicrobial properties identified a broad antimicrobial action against both gram-positive and gram-negative bacteria.

Overall evidence strength: Antimicrobial and antibiofilm findings for sundew constituents are supported by multiple in vitro studies. No human clinical trials evaluating sundew specifically for infection treatment were identified. Evidence is preliminary, confined to laboratory models.

5.3 Anticancer / Cytotoxic Properties of Plumbagin

Plumbagin shows significant cytotoxic potential against various cancer cell lines. Plumbagin is described as an important naphthoquinone with potent anticancer properties besides multitudinous uses in healthcare.

In eukaryotic cells, plumbagin evokes cell death, at least partially, via the generation of reactive oxygen species involving mitochondria.

Naphthoquinones are a group of highly reactive small molecules that are widely distributed in nature and have been shown to have cytotoxic effects due to the generation of reactive oxygen species within the cell.

Overall evidence strength: Anticancer effects attributed to plumbagin are based entirely on in vitro (cell line) and some animal studies. No clinical trials in humans have been identified for sundew or isolated plumbagin as a cancer treatment. Evidence is preliminary and pre-clinical.

5.4 Anti-inflammatory Use in Rheumatoid Arthritis (Plumbagin, Preclinical)

Research explored the effects of plumbagin on rheumatoid arthritis (RA). The RA cell model was simulated following treatment of interleukin-1β (IL-1β). After treatment of various concentrations of plumbagin, impact on cell viability was examined by MTT assay. A collagen-induced arthritis (CIA) model was also established. Plumbagin inhibited the viability of human fibroblast-like synoviocytes at the concentration of 1–3.5 µM. The inhibitory effect of 1 µM plumbagin on cell proliferation was similar to that of methotrexate, the drug used as the positive control.

Overall evidence strength: Purely preclinical — cell-based and animal model data only. No human clinical trial data for rheumatoid arthritis.

5.5 Antiparasitic Activity (Preclinical)

The naphthoquinone plumbagin was lethal for Leishmania donovani with an IC50 value of 0.3 µM. It abrogated the survival of S. mansoni with an IC50 value of 0.9 µg/mL, and was lethal for Fasciola gigantica with an IC50 value of 2.4 µg/mL. Plumbagin was also lethal for P. falciparum strains with IC50 values in the nanomolar range, and when given orally to mice at 25 mg/kg/day for 4 days, decreased P. berghei parasitemia by 41%.

Overall evidence strength: All data are in vitro or animal-model studies. No clinical trials have been identified.

6. Body Systems and Health Areas Associated with Sundew

• Respiratory system: Primary area of use. The ability of D. rotundifolia to relieve coughs and pulmonary diseases has been acknowledged for centuries in traditional medicine. Relevant conditions include bronchitis, whooping cough (pertussis), asthma, tracheitis, and dry or spasmodic cough.
• Immune and inflammatory system: The therapeutic activities have mainly been associated with two compound groups: flavonoids and naphthoquinones. The anti-inflammatory and antimicrobial activities of D. rotundifolia have been established.
• Antimicrobial / infectious disease: Some naphthoquinones and flavonoids, important secondary metabolites of Drosera, have also been considered antiviral. Activity has been demonstrated against bacteria, fungi, and parasites at preclinical level.
• Skin and wound healing (topical/external): Droserae herba is used in herbal medicines for the treatment of poorly healing, superficial wounds. Traditional topical uses include corns, warts, and burns.
• Oncology (preclinical only): Plumbagin's cytotoxic effects have been studied in cancer cell lines, but no clinical evidence exists.
• Antiparasitic (preclinical only): The plant produces the naphthoquinone plumbagin, which is a broad-spectrum antiparasitic principle as demonstrated in laboratory studies.

7. Dosage Forms and Reported Dosages

Dosage information for Droserae Herba derives primarily from pharmacopoeial sources and the German Commission E monograph rather than from clinical dose-finding trials. No standardized dosing range based on formal human pharmacokinetic or clinical efficacy studies has been established in the published literature identified.

• Dried herb (herbal tea): The average daily dose of Droserae herba is 3.0 g, mostly used in the form of tea infusions.
• Homeopathic preparation (case series): In a reported case series, three representative patients received 1 dose weekly of a 30c dilution of homeopathic pertussinum and a 6c dilution of homeopathic Drosera 3 times daily.
• In vitro concentrations (not clinical doses): Aqueous and ethanolic extracts inhibited human neutrophil elastase at IC50 values of 5 and 1 µg/mL, respectively, in laboratory assays.
• Plumbagin (animal/preclinical): In animal studies, plumbagin was given orally to mice at 25 mg/kg/day for 4 days to assess antiparasitic effects — this is not a human dosage.

One challenge is the intrinsic variability of plant compounds, which is influenced by environmental factors such as soil composition, precipitation patterns, and climatic conditions. Variations of compound concentrations that determine effectiveness can lead to over- or underdosing.

8. Safety Considerations

8.1 General Safety Profile

Safety evaluations through cytotoxicity tests in 3D cell cultures and the Galleria mellonella in vivo model confirmed the safety of sundew extracts used at antibiofilm concentrations.

At recommended amounts, sundew is thought to be safe. Higher levels may lead to gastrointestinal irritation in some people.

Internal use of this herb causes a harmless colouring of the urine.

8.2 Naphthoquinone Toxicity

Caution is advised especially regarding the naphthoquinone content of the different sundew species, as naphthoquinones such as plumbagin and 7-methyljuglone are known for cytotoxic effects.

Observed toxicity in laboratory studies may depend on the naphthoquinone content, which is higher in D. intermedia than in D. rotundifolia. Plumbagin showed very pronounced effects in toxicity studies and was 10–100 times more toxic than whole extracts and 7-methyljuglone.

Naphthoquinones are a group of highly reactive small molecules widely distributed in nature and shown to have cytotoxic effects due to the generation of reactive oxygen species within the cell. Due to their concentration-dependent cytotoxic effects, controlling the content of naphthoquinones is important for ensuring the safety of their application.

8.3 Species Variability and Quality Control

Quality parameters and testing procedures for sundew as a medicinal plant have recently been published, reflecting the need for standardization given variability among species and preparations. Currently there is no valid European Pharmacopoeia (Ph. Eur.) monograph for the quality control of Droserae Herba.

D. madagascariensis contains only about one-tenth of the flavonoids and ellagic acid derivatives and only one-percent of naphthoquinones compared to European sundew species like D. rotundifolia and D. intermedia. It appears that not every sundew species is equally suitable as a source for pharmaceutical use.

8.4 Conservation Status and Sourcing

Several species, including Plumbago, Drosera, and others, are being uprooted for the extraction of plumbagin by pharmaceutical industries, leading to destruction of natural habitats. The pharmaceutical industry is therefore facing an acute shortage of plant material. The successful sustainable cultivation of sundew on rewetted peatlands not only leads to the preservation of natural populations, but also provides a basis for the sustainable pharmaceutical use of the plant.

8.5 Pregnancy and Lactation

Pregnant and breast-feeding women should avoid use of sundew. This precaution appears in available reference sources, though no published clinical data specifically characterizing reproductive safety were identified in the peer-reviewed literature retrieved.

8.6 Potential Drug Interactions

No specific drug interaction studies were identified in the peer-reviewed literature. Naphthaquinones are believed to give sundew its antispasmodic effect; these naphthaquinones include plumbagin, ramentone, and related compounds. Given the known pharmacological activities on muscarinic M3 receptors and phosphodiesterase isoforms identified in laboratory studies, theoretical interactions with anticholinergic medications or PDE inhibitor drugs may be plausible but have not been studied clinically.

9. Conservation and Regulatory Status

The traditional medicinal plant sundew (Drosera sp.) has disappeared from mainstream therapy due to nature conservation pressures, but can now be cultivated sustainably on rewetted peatland. The main European species — D. rotundifolia, D. intermedia, and D. anglica — are now rarely used in commercial preparations due to threat of extinction. In many European jurisdictions, wild collection of these species is prohibited or heavily restricted.

The drug Droserae Herba, traditionally produced from the dried aerial parts of the plant, is accepted in various pharmacopeias of the world. The German Commission E has issued a positive monograph for Droserae Herba for irritable and whooping cough. A formal European Pharmacopoeia monograph for quality control does not yet exist as of recent publications.

References

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