Scleranthus annuus (Annual Knawel): A Comprehensive Reference
1. Identity and Botanical Description
Nomenclature and Taxonomy
Scleranthus annuus is a species of flowering plant in the family Caryophyllaceae known by the common names German knotweed and annual knawel. The species was first formally described and named by Carl Linnaeus, appearing in his Species Plantarum of 1753. Its full taxonomic placement situates it within the order Caryophyllales, family Caryophyllaceae, tribe Sclerantheae, genus Scleranthus.
Scleranthus, the knawels, are a genus of herbaceous plants in the family Caryophyllaceae, with about 12 species native to Europe, Siberia, western Asia, north Africa, Ethiopia, New Guinea, and Australia. Within this genus, the genus Scleranthus L. comprises 11 named species divided into two sections, Scleranthus and Mniarum; section Scleranthus includes three endemic species to Europe, Western Asia, and North Africa — S. annuus, S. perennis, and S. uncinatus — as well as three Australian endemic species.
Scleranthus annuus L. (Annual Knawel) is a widely accepted species, though its limits are constantly under review; some treatments include within it S. polycarpos L. as S. annuus subsp. polycarpos Bonnier & Layens. Plants of the World Online (Kew Science) additionally recognises subspecies aetnensis and collinus. The chromosome number is 2n = 44 (Stace 2010).
Common synonyms and variant names encountered in older literature include Knavel annuum (L.) Scop. and Scleranthus biennis Reut. The common name "knawel" is derived, from the 16th-century German Knauel for knotweed, literally meaning "ball of yarn."
Morphology
Scleranthus annuus is an annual or biennial herb with low, much-branched spreading stems up to 15 cm (6 in) long growing from a taproot. The leaves are needle-like or linear in shape with sharp, stiff points, oppositely arranged in pairs about the stem and fused together at the bases.
Flowers occur in pairs or small clusters of up to five; the flowers lack petals but have bell-shaped calyces of green petal-shaped sepals. The flowers measure about 4 mm in diameter and do not have any petals; the sepals have five points and often may be mistaken for petals, appearing like a minute crown.
Geographic Distribution and Habitat
The species is native to Europe, Asia, and North Africa, and it is known throughout the rest of the temperate world as an introduced species and a common weed. More specifically, the native range of this species spans Macaronesia, Europe to Central Siberia, the Mediterranean region to Iran and the Arabian Peninsula; it is an annual or biennial and grows primarily in the temperate biome.
It is widespread throughout Britain, but absent from the very north and the Outer Hebrides; in Ireland it is rare but scattered throughout. The species occurs throughout Europe except in the extreme north and has been introduced to North and South America, Australia, and elsewhere.
It grows in soil pockets among rocks, on bare places, on disturbed sandy soil on heaths, in arable fields, in sand pits, in quarries, and occasionally on shingle on the coast or beside rivers. It prefers sandy and gravelly soils and is drought tolerant, but tolerates moist sites and sun to partial shade.
In the UK, intensive arable farming with increased use of broad-spectrum herbicides has led to its decline and it is regarded as endangered in the wild. Subspecies annuus is classified as Endangered in Britain, facing a very high risk of extinction in the wild in the near future.
2. Traditional and Historical Use
European Folk Medicine
Scleranthus annuus has been used in traditional herbal medicine, although specific applications are not well documented. It is more renowned for its hardy, weedy characteristics rather than its medicinal properties. It is harvested from the wild for local use as a medicine.
Knawel has been used as a cure for toothache and the sweet-tasting leaves are fairly good fodder for sheep. This represents one of the few specifically documented traditional applications of the plant as a crude herbal remedy.
Historically, Scleranthus annuus has been utilized for its potential medicinal properties, though specific details on its applications are scarce. The North Carolina State Extension notes that the plant has been used in ethnobotany and herbal medicine.
Caucasus Ethnobotanical Context
Academic ethnobotanical work on the Caucasus region has documented Scleranthus annuus within local traditional systems. A scholarly chapter on Scleranthus annuus L. and Scleranthus perennis L. within the Caryophyllaceae family appears in Bussmann, R.W. (ed.), Ethnobotany of the Caucasus, Ethnobotany of Mountain Regions, Springer, Cham (2024). The full text of the chapter is behind a paywall and its specific reported uses could not be independently verified from open sources.
The Bach Flower Remedy System (Early 20th Century)
By far the most widely discussed contemporary use of Scleranthus annuus as a supplement or remedy is within the Bach Flower Remedy system. A range of flower remedies were discovered by the English bacteriologist and physician Edward Bach, born in Moseley, Birmingham, on 24 September 1886; pioneering books he authored in 1925 and 1931 provided a framework for the analysis of psychological and emotional correlates of physical diseases.
Created in the 1930s by Dr. Edward Bach, he believed emotional wellbeing is fundamentally connected to health. Scleranthus is described as one of Bach's original twelve healers, prepared by the sun method. Within this system, the essences of particular flowers are prescribed for conditions such as indecisiveness and mood swings (Scleranthus), among many others.
Bach experimented with highly diluted derivatives of wildflower species obtained by boiling the flowering sprays, leaves, and twigs in natural spring water (the "boiling method") or placing flower heads and spring water in direct sunlight (the "sun method"); the boiling method involves filtering the remaining liquid. Specifically for Scleranthus, the Bach Flower Remedy is prepared by employing the sun method: the flowering heads are collected and then floated on the surface of water kept in a bowl.
The 38 Bach Flower Remedies fall into seven broad categories, each addressing specific emotional and psychological challenges. Scleranthus falls within the "uncertainty" category, prescribed specifically for indecision.
Flower essences of annual knawel are occasionally used by herbalists to treat indecision or mood swings, and the plant is associated with anthropogenic (human-disturbed or -maintained) habitats, meadows and fields.
3. Key Constituents and Active Compounds
Overview of Phytochemistry
Phytochemical research on Scleranthus annuus remains limited. Scleranthus perennis L. and Scleranthus annuus L. belong to the Caryophyllaceae family and are endemic species to Europe, North Africa, and Western Asia; only a few studies have reported on the phytochemical description of these plants. The substances previously isolated from S. annuus were mostly phenolic acids and phytoecdysteroids, as well as flavonoids.
More specifically, S. annuus water/alcoholic extracts are a source of phenolic acids and flavonoids; S. perennis has not been well studied, and thus its phytochemical and pharmacological data are scarce. This assessment, from a peer-reviewed study published in PMC, also broadly applies to S. annuus given the paucity of research.
Flavonoids
Flavonoids are polyphenolic compounds that remain one of the most extensively studied constituents of the Caryophyllaceae family, with numerous structurally diverse aglycones including flavones, flavonols, flavanones (dihydroflavones), and flavonols documented across species.
A 2022 peer-reviewed study (Molecules, PMC) conducted phytochemical quantification on both S. annuus and S. perennis. Several flavone C-glycosides were identified and isolated from these Scleranthus species, including lucenin-1 (5,7,3′,4′-tetrahydroxyflavone-6-C-xyloside-8-C-β-d-glucoside), vicenin-2 (5,7,3′-trihydroxyflavone-6-C-glucoside-8-C-β-d-glucoside), and chrysoeriol-6-C-β-d-glucopyranoside-8-C-α-arabinopyranoside. The quantification results showed that the S. annuus fractions are rich sources of flavonoids.
Phenolic Acids and Phytoecdysteroids
To date, the allocated substances previously isolated from S. annuus were mostly phenolic acids and phytoecdysteroids, as well as flavonoids. Phytoecdysteroids are a class of polyhydroxylated steroids structurally analogous to insect moulting hormones; their presence in S. annuus aligns with their broader occurrence across the Caryophyllaceae family.
The most important classes of phytochemicals within the Caryophyllaceae family include saponins, phytoecdysteroids, other sterols, flavonoids, lignans, other polyphenols, essential oils, and nitrogen-containing compounds such as vitamins, alkaloids or cyclopeptides. While this characterisation applies to the family broadly, only phenolic acids, phytoecdysteroids, and flavonoids have been specifically reported in S. annuus in the available peer-reviewed literature.
Compounds in the Bach Flower Preparation
In its commercial dosage form, the active ingredient is listed as Scleranthus (Scleranthus annuus) at a 5X HPUS (Homeopathic Pharmacopoeia of the United States) potency, with the inactive ingredient being a 27% grape alcohol solution. At such extreme homeopathic dilutions, it is chemically implausible that meaningful concentrations of any phytochemical constituent would remain in the final preparation.
4. Mechanisms of Action
Anti-Collagenase Activity (In Vitro)
The only experimentally characterised mechanisms for Scleranthus extracts derive from in vitro laboratory research. Factors with the ability to inhibit collagenase or elastase activity have an advantageous impact for supporting skin health through the prevention of dermal matrix degradation; researchers therefore investigated anti-collagenase substances from both S. perennis and S. annuus.
The highest percentage of collagenase inhibition (at 400 µg/mL) was distinguished for methanolic extracts (22.06%, 32.04%) and ethyl acetate fractions (16.59%, 14.40%) from S. annuus and S. perennis, respectively. Isolated compounds 6–9 displayed moderate inhibitory activity, with IC50 values ranging from 39.59–73.86 µM. These findings are preliminary and in vitro only; no human or animal data on this mechanism exists.
Antioxidant Activity (In Vitro)
The anti-collagenase and antioxidant activities of all isolated compounds obtained from extracts and fractions from both Scleranthus species were evaluated in the same 2022 study. The antioxidant potential of the flavonoid-rich fractions was assessed alongside the enzyme inhibition studies. No clinical translation of these in vitro antioxidant findings has been reported in the peer-reviewed literature.
Posited Mechanism in the Bach System
In the Bach Flower Remedy system, a plant's "unlocked energy" is considered as therapeutically important as its biodynamic chemical components. This concept has no basis in conventional pharmacology. The proposed mechanism — that vibrational or energetic imprints from the flowers, transferred to water, act on emotional states — is not supported by any peer-reviewed mechanistic evidence.
5. Scientific Evidence by Area of Use
5.1 Emotional States and Psychological Applications (Bach Flower Use)
The primary contemporary claim for Scleranthus annuus as a supplement or remedy is its role in the Bach Flower system for indecision and mood swings. The scientific evidence for this use has been reviewed in multiple systematic analyses.
Systematic Review (Ernst, 2010, Swiss Medical Weekly): Bach flower remedies continue to be popular and proponents make a range of medicinal claims for them. A systematic review aimed to critically evaluate the evidence for these claims. Five electronic databases were searched without restrictions on time or language. All randomised clinical trials of flower remedies were included. Seven such studies were located. All but one were placebo-controlled. All placebo-controlled trials failed to demonstrate efficacy. It was concluded that the most reliable clinical trials do not show any differences between flower remedies and placebos.
Systematic Review (Thaler et al., 2009, BMC Complementary and Alternative Medicine): MEDLINE, Embase, AMED, and the Cochrane Library were searched from inception until June 2008. For efficacy, all prospective studies with a control group were included; for safety, retrospective observational studies with more than 30 subjects were also included. Two authors abstracted data and determined risk of bias. Four randomised controlled trials (RCTs) and two additional retrospective, observational studies were identified. Three RCTs of Bach Flower Remedies for students with examination anxiety, and one RCT of BFRs for children with attention-deficit hyperactivity disorder (ADHD), showed no overall benefit in comparison to placebo. Due to the number and quality of the studies, the strength of the evidence is low or very low.
Studies that assessed efficacy of Bach Flower Remedies were conducted in the UK, Germany, Israel, and the USA in students with examination anxiety or children with attention-deficit hyperactivity disorder (ADHD).
A specific double-blind, placebo-controlled study is documented in the literature: a double-blind, placebo-controlled study tested whether a particular combination of Bach flower remedies could relieve the anxiety that students experience while taking exams; the trial used a mixture containing ten flower extracts, including scleranthus, as suggested by an expert in the use of Bach flower remedies. Sixty-one students were enrolled; fifty-five completed the study.
Overall evidence characterisation: There is no scientific evidence that any Bach flower remedy produces a medicinal effect, and there is some evidence that the method does not work. Further research is needed to explore the potential mechanisms by which Bach Flower Remedies may work, particularly within the context of psychological and emotional healing. Studies that examine the placebo effect and the psychological aspects of belief in healing could help clarify whether Bach remedies work primarily through mental processes rather than a direct physical effect.
5.2 Skin Health / Anti-Collagenase Activity
As described in the mechanisms section, in vitro evidence from a 2022 study published in the journal Molecules (PMC accession PMC8951040) demonstrated that methanolic extracts of S. annuus inhibit collagenase activity at concentrations of 400 µg/mL. Collagenase inhibition is considered advantageous for supporting skin health, through the prevention of dermal matrix degradation. However, this evidence is entirely pre-clinical (in vitro), and no human trials or animal studies examining topical or internal use of S. annuus for skin health endpoints have been identified in the peer-reviewed literature. Evidence strength: very preliminary; in vitro only.
5.3 Antioxidant Properties
The same 2022 PMC-indexed study evaluated the antioxidant potential of isolated flavone C-glycosides from both Scleranthus species. The quantification results showed that S. annuus fractions are rich sources of flavonoids with antioxidant activity. Again, this evidence is in vitro and does not provide a basis for clinical claims. No human trials on antioxidant effects of S. annuus extracts have been identified.
5.4 Traditional Uses (Toothache, Digestive Applications)
Knawel has been used as a cure for toothache in traditional herbal practice, but no clinical or even pre-clinical studies investigating this use have been identified in the peer-reviewed literature. Traditional applications of Scleranthus annuus in herbal medicine are not well documented. These uses are purely historical and anecdotal.
6. Body Systems and Health Areas Associated with Scleranthus annuus
- Psychological / Neurological System: Scleranthus is indicated in the Bach system for indecisiveness and mood swings — the most widely cited application in the supplement context. No clinical evidence supports pharmacological action on the central nervous system.
- Integumentary System (Skin): In vitro evidence suggests potential anti-collagenase activity relevant to dermal matrix preservation, but no human skin health studies exist.
- Antioxidant Defence: In vitro antioxidant activity has been demonstrated for flavonoid-containing fractions. Clinical relevance is unknown.
- Digestive System: Traditional folk use has included the plant as a digestive agent, but this is undocumented in peer-reviewed literature.
- Oral Health: Historical use as a remedy for toothache is documented in ethnobotanical sources without clinical substantiation.
7. Dosage Forms and Reported Dosages
Bach Flower Remedy (Commercial Form)
The predominant commercial preparation of Scleranthus annuus as a supplement is the Bach Flower Remedy. The active ingredient is a 5X dilution of Scleranthus (Scleranthus annuus) HPUS, with the inactive ingredient being 27% alcohol.
Dosage as stated on the product label: Take 2 drops in a small glass of water and sip at intervals, or add to a 30 ml mixing bottle containing water. Take 4 drops a minimum of 4 times a day. An alternative stated dosage from another manufacturer specifies 2 drops of a single remedy directly on the tongue or added to a beverage and sipped.
Homeopathic product claims are based on traditional homeopathic practice, not accepted medical evidence.
Research Extracts (In Vitro Context Only)
In the 2022 in vitro anti-collagenase study, the highest percentage of collagenase inhibition was measured at concentrations of 400 µg/mL for methanolic extracts and ethyl acetate fractions from S. annuus. Isolated flavone C-glycoside compounds displayed moderate inhibitory activity with IC50 values ranging from 39.59–73.86 µM. These concentrations relate to laboratory assay conditions and do not correspond to any human dosage.
Preparation Form in Studies
All phytochemical and biological activity studies identified in the peer-reviewed literature used crude plant material (aerial parts) extracted using methanol, ethanol/water mixtures, or fractionated into ethyl acetate and butanol fractions, followed by chromatographic isolation. No human clinical trial for any phytochemical application of S. annuus has been conducted.
8. Safety Considerations and Known Interactions
Toxicity Profile
Scleranthus annuus is not known to be toxic to humans. No formal toxicological studies (acute, subacute, chronic, or reproductive toxicity) on this species have been identified in peer-reviewed databases. Due to its limited use in culinary or medicinal applications, any potential adverse effects are not well documented.
Scleranthus annuus is not listed as toxic to dogs and cats; however, as with any plant, it is advisable to prevent pets from consuming it in large quantities to avoid any digestive discomfort.
Safety of the Bach Flower Preparation
The Bach Flower preparation form is prepared at extreme homeopathic dilutions (5X HPUS) in an alcohol vehicle. Four RCTs and two retrospective, observational studies of Bach Flower Remedies identified in a systematic review found no overall benefit in comparison to placebo, and due to the number and quality of studies, the strength of the evidence is low or very low. The systematic review literature did not identify serious adverse effects attributable to Bach Flower Remedies at standard dilutions.
Alcohol Content
Commercial Bach Flower preparations contain 27% grape alcohol as the inactive ingredient. This is of note for individuals who are intolerant of alcohol, including those with alcohol use disorder, certain religious prohibitions, or conditions sensitive to ethanol.
Absence of Pharmacokinetic Data
No pharmacokinetic studies — covering absorption, distribution, metabolism, or excretion — of any extract or constituent of Scleranthus annuus in humans or animals have been identified in the peer-reviewed literature. This absence means that meaningful statements about bioavailability, half-life, or drug interactions cannot be made.
Drug Interactions
No peer-reviewed evidence of drug interactions involving Scleranthus annuus extracts, preparations, or isolated constituents has been identified. Given the extreme dilution of the homeopathic preparation and the total absence of pharmacokinetic data for any more concentrated form, no interaction data can be presented.
Conservation Status and Wild Harvesting
In the UK, intensive arable farming with increased use of broad-spectrum herbicides has led to its decline and it is regarded as endangered in the wild. Subspecies annuus is classified as Endangered in Britain (facing a very high risk of extinction in the wild in the near future), while subspecies polycarpos is National Scarce. Wild harvesting for supplement production therefore raises conservation concerns in some regional contexts.
9. Summary of Evidence Quality
The overall evidence base for Scleranthus annuus as a dietary supplement or medicinal ingredient is extremely limited. Its primary usage context — the Bach Flower Remedy system — has been assessed in multiple systematic reviews, all of which conclude that all placebo-controlled trials of flower remedies failed to demonstrate efficacy, and the most reliable clinical trials do not show any differences between flower remedies and placebos. Phytochemical research has confirmed the presence of phenolic acids, phytoecdysteroids, and flavonoids with in vitro anti-collagenase and antioxidant activity, but only a few studies have reported on the phytochemical description of these plants and no human clinical evidence for any pharmacological effect exists. Traditional ethnobotanical use is historically sparse and poorly documented. In the absence of human clinical trials, controlled pharmacological studies, or formal toxicological assessments, no evidence-based conclusions about the efficacy or safety of Scleranthus annuus as a supplement can be drawn beyond what has been stated in the peer-reviewed literature reviewed here.
References
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