IngredientsBush Monkey Flower (Diplacus aurantiacus) is a flowering plant that grows in a subshrub form, native to western North America from southwestern Oregon south through Northern and Central California. It is a member of the lopseed family, Phrymaceae, and was formerly known as Mimulus aurantiacus.
The plant's taxonomy has undergone considerable revision and remains a subject of ongoing botanical debate. There are many regional variants with intergrading hybrids; between one and thirteen species have been recognized in California. This uncertainty as to species' boundaries is confounded by the fact that, as of 2018, bush monkeyflower is listed both in the genus Mimulus and in the genus Diplacus. The taxonomy of the group was thoroughly revised to better reflect evolutionary relationships, and many species were moved from Mimulus (now 7 species) to Erythranthe (111 species), Diplacus (46 species), and certain small genera.
Additional synonyms applied to the species and its close variants include Mimulus bifidus, Diplacus bifidus, Mimulus aurantiacus, and Mimulus aurantiacus var. aurantiacus. Many formerly identified species and subspecies of Mimulus were combined into Mimulus aurantiacus, including M. longiflorus, M. longiflorus rutilus, and M. puniceus.
The genus name has two possible etymological roots. The genus name Diplacus derives from the Greek words "diplo" meaning "double" and "akos" meaning "a point," which may refer to the plant's distinctive flower shape. Mimulus owes its common name to the shape and colors of its flowers that suggest "mime" (Latin "mimus"), a monkey's face. The species name aurantiacus comes from the Latin word "aurantiacus," meaning "orange," reflecting the vivid hues of its flowers that resemble the fruit of the orange tree.
The plant grows up to 1.2 meters (4 feet) tall, has deep green, sticky leaves 3 to 7 centimeters long and up to a centimeter broad, and flowering stems that grow vertically. The flowers are tubular at the base and about 2 centimeters long with five broad lobes; they occur in a variety of shades from white to red, the most common color being a light orange. The bright orange color of the flowers, sticky undersides of the leaves, and shrubby growth habit make sticky monkey flower easy to distinguish from the red scarlet monkey flower (M. cardinalis) and the yellow common monkey flower (M. guttatus).
The stickiness of the leaves and sepals comes from glandular secretions. This resin, which makes up almost 30% of the leaf's weight, helps to lessen the impact of herbivorous feeding. The plant is an important host plant for the larvae of the common buckeye butterfly (Junonia coenia) and the variable checkerspot (Euphydryas chalcedona), despite the phenolic resin in the leaves which deters feeding. This resin also helps the plant retain water in dry environments.
The sticky monkey flower grows in the scrub and chaparral from Mendocino to Baja. It grows in many climates and will thrive in many types of soil — wet, dry, sandy, or rocky — and it even grows in serpentine, a soil that most plants have difficulty thriving in because of its unique mineral composition.
The use of Bush Monkey Flower in traditional medicine is primarily documented among Indigenous peoples of California. The Miwok and Pomo Native Americans used the plant to treat minor ailments such as sores, burns, diarrhea, and eye irritation, and they used the colorful flowers for decorative purposes.
Reportedly, the Kumeyaay tribe used monkey flower primarily for medicinal purposes, from poultices for burns and wounds to treatments for colds, coughs, flus, stomach disorders, and heart ailments. Some Native Americans used the young stems and leaves of monkeyflower for salad greens.
Young Mimulus leaves may be eaten in salads, though the older leaves may be eaten as well but grow bitter with age.
Traditional preparations documented among California tribes included topical poultices applied directly to the skin for wounds and burns, as well as internal preparations for gastrointestinal ailments. The leaves, stems, flowers, and roots were all variously employed, depending on the tribe and the condition being treated. External preparations — especially for skin sores, burns, and eye irritation — appear to have been the most consistent cross-tribal use. The astringent tannin-rich resin of the leaves was likely central to the wound-healing and anti-diarrheal applications.
In the twentieth century, the genus Mimulus entered a distinct complementary medicine tradition. The Bach™ Original Flower Remedies were developed in the 1920s and 1930s by Dr. Edward Bach in England, as a system of 38 essences which Dr. Bach believed offered a holistic approach to achieving emotional balance. The Mimulus remedy is designated for known fears. Whenever a person is frightened or anxious about something and can name what that "something" is, Mimulus is the remedy indicated. Mimulus fears are those of everyday life: fear of public speaking, of the dark, of aggressive dogs, of illness and pain.
It should be noted that the Bach Flower Remedy labeled "Mimulus" is prepared primarily from Mimulus guttatus (yellow monkey flower), not specifically from Diplacus aurantiacus. The product is described on the FDA's DailyMed database as a homeopathic preparation derived from Mimulus guttatus flowering top solution.
The most pharmacologically significant and extensively studied phytochemicals of Diplacus aurantiacus are concentrated in the sticky leaf surface resin. The chaparral subshrub produces leaf surface resins in excess of 30% of leaf dry weight. The resin provides some defense against insect herbivores and perhaps from desiccation and injury from UV light. The resin comprises six flavanones and an α-pyrone.
The leaf surface resin has been found to contain several flavonoids. The predominant leaf surface flavonoids were characterized as the terpenoid flavanones mimulone, diplacone, 3′-O-methyldiplacone, diplacol, and 3′-O-methyldiplacol. Less abundant flavonoids of the leaf surface were determined to be 3-geranyl-4-hydroxy-6-(2-hydroxypropyl)-2-pyrone, and eriodictyol 7, 3′-dimethyl ether.
The structural relationships among these key compounds have been precisely characterized. Five of the resin components previously isolated from M. aurantiacus are closely related flavanones, all with a terpenoid side chain. The least substituted of these terpenoid flavanones is mimulone. The 3′-hydroxy analog of mimulone is diplacone, and the 3′-methoxy analog of mimulone is 3′-O-methyldiplacone. The remaining two terpenoid flavanones are the 3-hydroxy analogs of diplacone and 3′-O-methyldiplacone. The 3-hydroxy analog of diplacone is diplacol, and the 3-hydroxy analog of 3′-O-methyldiplacone is 3′-O-methyldiplacol.
Two major pigment types determine flower color in Mimulus: anthocyanins are responsible for the pink/purple color, and carotenoids for the yellow. These pigments are of interest as antioxidant compounds, though their concentrations vary considerably across the species' diverse color morphs.
Proposed roles for the leaf surface flavonoids of Mimulus aurantiacus include protection from desiccation, UV light protection, and resistance to insects. The different components may differ in their ecological roles, and methoxylated components may be most effective as antidesiccants.
The geranylflavanone production was inherited with dominance or over-dominance, suggesting that the quantity of each geranylflavanone is not simply inherited via the independent additive action of many genes of small effect. This genetic complexity in phytochemical production has implications for the consistency of phytochemical content among plant populations used in herbal preparations.
The most systematically studied pharmacological activity of D. aurantiacus phytochemicals is anti-inflammatory activity. Diplacone and mimulone, two geranylated flavanones from this plant, have previously shown anti-inflammatory and antiradical activity in vitro.
An animal study published in a peer-reviewed journal investigated whether these effects translated to in vivo models. This study evaluated diplacone and mimulone activity in vivo on a model of colitis induced in Wistar rats by an oral administration of dextran sulfate sodium (DSS). Diplacone and mimulone were administered at a bolus dose of 25 mg/kg by gastric gavage 48 and 24 hours prior to the induction of colitis by DSS, and every 24 hours on the following days of the experiment. The effect of treatment was assessed by monitoring the disease activity index, histopathological examination, evaluation of the weight and length of the colon, and by analysis of the levels and activities of COX-2, MMP2, SOD2, and catalase in the inflamed tissue. Administration of the test compounds prior to and after induction of colitis ameliorated the symptoms of colitis.
Strength of evidence: This is animal (rodent) model data only. No human clinical trials have been identified for the anti-inflammatory effects of D. aurantiacus extracts or its isolated geranylflavanones. The in vitro and animal findings are hypothesis-generating but cannot be extrapolated to efficacy in humans.
Mimulone and diplacone have been evaluated for neuroprotective properties in in vitro cell systems. Researchers evaluated the in vitro neuroprotective and anti-aggregative properties of the geranylated flavonoid cannflavin A (from cannabis) against amyloid-β (Aβ1–42) and compared it to two similarly geranylated flavonoids, mimulone and diplacone, to compare the bioactive properties of these unique flavonoids more broadly. Neuronal viability was assessed in PC12 cells biochemically using the MTT assay in the presence of each flavonoid (1–200 µM) for 48 hours.
The results were mixed for the D. aurantiacus-derived compounds. Neither mimulone nor diplacone exhibited a neuroprotective hormetic effect; instead they showed only concentration-dependent neurotoxicity, with diplacone the more potent (from greater than 1 µM).
A separate cell-based study reported more nuanced findings. The neuroprotective effects of mimulone and diplacone against glutamate-induced neurotoxicity were studied in primary cultured rat cortical cells. It was found that only diplacone weakly attenuated glutamate-induced toxicity at 10 µM.
Diplacone also protected premature senescent human embryonic lung diploid fibroblast cells at 10 µM from ageing induced by H₂O₂.
Strength of evidence: All neurological evidence is in vitro (cell culture only). Results are mixed — at higher concentrations the isolated compounds show cytotoxicity rather than protection. No animal or human clinical studies of neuroprotection have been identified.
The C-geranylated flavanones characteristic of the Mimulus/Diplacus genus have demonstrated in vitro antiparasitic activity. A study on the related species Mimulus bigelovii, which shares the same class of geranylated flavanones, reported: all compounds showed moderate antileishmanial activity against axenic Leishmania donovani amastigotes with IC₅₀ values ranging from 4.8 to 14.6 µg/mL. Bioactivity-directed fractionation of the MeOH extract of Mimulus bigelovii resulted in the isolation of four C-geranyl flavanones, diplacone, 3′-O-methyldiplacone, 4′-O-methyldiplacone, 3′-O-methyldiplacol, together with a geranylated flavone, cannflavin A.
For the D. aurantiacus-derived compounds specifically, the antiparasitic activities of C-geranylated flavonoids mainly involved the effects of seven unmodified C-geranylflavanones on Leishmania species, including mimulone, diplacone, 3′-O-methyldiplacone, and 3′-O-methyldiplacol. Compounds 3′-O-methyldiplacone and 3′-O-methyl-5′-O-methyldiplacone achieved significant antileishmanial activity with IC₅₀ values of 10.4 and 12.7 µM against L. donovani, and 11.3 and 8.0 µM against L. braziliensis, respectively, compared with 9.5 and 6.7 µM of miltefosine as the positive control. Furthermore, diplacone was also active (IC₅₀ 1.4 µg/mL) against the related kinetoplastid parasite Trypanosoma brucei brucei.
Strength of evidence: In vitro only. No animal or human studies have tested the antiparasitic potential of D. aurantiacus extracts or their isolated compounds in vivo.
A patent application (US20050152996, filed 2005) proposed the use of Mimulus aurantiacus extracts for treating psoriasis. The invention provides extracts of the plant Mimulus aurantiacus for use in the treatment of a wide variety of skin ailments, and in particular to alleviating psoriasis. The compositions include Mimulus aurantiacus extracts that can be used topically, and can be formulated as lotions, oils, shampoos, soaps, sprays, creams, salves, foams, or gels.
This patent appears in the scientific literature as a cited reference in a review of plants with potential antipsoriatic activity, published in a peer-reviewed pharmacognosy journal. Butler (2005) filed a US patent application on extracts of Mimulus aurantiacus for treating psoriasis and repelling insects. However, the citations to this patent in the peer-reviewed literature are bibliographic references only; no published controlled clinical trial data in humans evaluating Mimulus aurantiacus for psoriasis has been identified in the peer-reviewed literature.
Strength of evidence: Patent-level claims only, with ethnobotanical plausibility (wound, burn, and skin sore uses in traditional medicine). No peer-reviewed clinical evidence. The traditional use of poultices for burns, sores, and skin irritation by Miwok, Pomo, and Kumeyaay peoples represents historical empirical use, not tested efficacy.
The same patent also provides extracts of the plant Mimulus aurantiacus for use as insect repellants that are described as biodegradable and non-toxic to humans and animals. Insect-repelling compositions including Mimulus aurantiacus extracts can be formulated as powders, sprays, or mulches for use on plants, or as lotions, sprays, shampoos, soaps, creams, salves, foams, or gels for use on humans or animals.
The basis for this application lies in the phytochemical ecology of the plant itself. This resin provides some defense against the insect herbivore Euphydryas chalcedona and may also protect plants from desiccation and UV light injury. Nearly 30% of the dry weight of leaves of the chaparral subshrub comprises leaf surface resins.
Strength of evidence: Preclinical (ecological and in vitro data) plus patent-level claims. No published controlled study on insect repellency in humans has been identified.
The geranylated flavanones present in D. aurantiacus include ortho-dihydroxy substituted compounds (diplacol, diplacone) which, based on the broader flavonoid pharmacology literature, are structurally predicted to have free-radical scavenging capacity. Thirteen C-geranylated flavonoids isolated from related Paulownia species had been evaluated for their antioxidant activity on HUVEC injury induced by homocysteine or H₂O₂, and some compounds caused improved proliferative activity at 10 µM; however, at 20 µM or higher, diplacone expressed cytotoxic activity to HUVECs and reduced its proliferative activity. This finding highlights a dose-dependent complexity — antioxidant/cytoprotective at low concentrations and potentially cytotoxic at higher concentrations.
Strength of evidence: In vitro studies on isolated compounds, with a cytotoxicity signal at higher doses. No human evidence.
Within the Bach Flower Remedy system, Mimulus preparations have been used for anxiety and fear. A systematic review of Bach Flower Remedies published in a peer-reviewed journal evaluated the evidence base for this tradition. One German study randomized 61 students to a pre-determined combination of 10 Bach Flower Remedies (including mimulus, impatiens, gentian, chestnut bud, rock rose, larch, cherry plum, white chestnut, scleranthus, and elm) or placebo in a four-week cross-over design. Another RCT conducted in the UK randomized 100 students to at least one week of Five Flower Rescue Remedy or placebo. Both trials did not detect any differences in efficacy between Bach Flower Remedies and placebo for the treatment of examination anxiety.
Bach flower remedies are very diluted preparations of different species of wildflowers, created by Dr. Edward Bach in the 1930s. Bach flower remedies are often so diluted that they contain little or no detectable amounts of active ingredients. People use Bach flower remedies for anxiety, depression, ADHD, pain, and many other conditions, but there is no good scientific evidence to support these uses.
Strength of evidence: Randomized controlled trials show no significant difference from placebo for the anxiety-related applications of Bach Flower Remedies containing Mimulus. The FDA has not evaluated Bach Flower Remedies for safety or efficacy.
Traditional use involved topical poultices prepared from fresh leaves and flowers applied directly to the skin for burns, wounds, and sores. Internal preparations for diarrhea, stomach ailments, and respiratory conditions were also documented among California tribes, though specific preparation methods and quantities were not standardized and have not been precisely recorded in the available ethnobotanical literature.
The patent-described compositions include Mimulus aurantiacus extracts formulated as lotions, oils, shampoos, soaps, sprays, creams, salves, foams, or gels for topical application to the skin. No specific concentrations or application frequencies were disclosed in the publicly accessible summary of this patent.
In the rat colitis model, diplacone and mimulone were administered at a bolus dose of 25 mg/kg by gastric gavage, given 48 and 24 hours prior to the induction of colitis by DSS, and every 24 hours on the following days of the experiment. This is an animal study dosage and cannot be directly translated to human dosing.
In cell culture studies, neuronal viability was assessed in PC12 cells in the presence of each flavonoid at concentrations of 1–200 µM for 48 hours. It was found that diplacone weakly attenuated glutamate-induced toxicity at 10 µM in primary cultured rat cortical cells. These are laboratory concentrations used for mechanistic research and are not clinical dosing recommendations.
Directions for Bach Flower Remedy use instruct users to place 2 drops in water and sip at intervals. For combination use, 2 drops of each essence (maximum 7 essences) are added to a mixing bottle containing still spring water, and 4 drops are taken 4 times a day.
The in vitro evidence raises concentration-dependent cytotoxicity concerns for the geranylflavanones characteristic of this plant. Neither mimulone nor diplacone exhibited neuroprotective effects in PC12 cell studies; instead, they showed only concentration-dependent neurotoxicity, with diplacone the more potent (from greater than 1 µM).
At concentrations of 20 µM or higher, diplacone expressed cytotoxic activity to human umbilical vein endothelial cells (HUVECs) and reduced their proliferative activity. These findings are from isolated pure compounds in cell culture and the relevance to whole-plant extracts applied topically or consumed in traditional quantities is unknown, but they indicate a need for caution in any attempt to concentrate or isolate these compounds.
When taken by mouth, Bach flower remedies are possibly safe when used in moderation. Since most Bach flower remedies contain little or no active ingredient, these products are not expected to cause harm. But they are preserved in brandy and therefore contain alcohol. Bach flower remedies are likely unsafe when taken by mouth while pregnant or breast-feeding because they contain alcohol. Alcohol can cause birth defects and other harm to infants, and the alcohol in these preparations also passes into breast milk and can interfere with the infant's development.
Bach flower remedies contain alcohol. When disulfiram is taken within 12 hours of alcohol it can cause a reaction. Bach flower remedies should not be taken by individuals taking disulfiram.
No monograph for Diplacus aurantiacus / Mimulus aurantiacus has been identified in the WHO traditional medicine monographs, the European Pharmacopoeia, ESCOP, the German Commission E, or the NIH Office of Dietary Supplements databases. The plant is not currently the subject of an NIH National Center for Complementary and Integrative Health (NCCIH) summary. This means there is no regulatory consensus on safe dose ranges, contraindications, or quality standards for commercial preparations of this plant.
The FDA's DailyMed database notes that homeopathic products derived from Mimulus have not been evaluated by the Food and Drug Administration for safety or efficacy, and the FDA is not aware of scientific evidence to support homeopathy as a treatment modality.
No controlled safety studies in pregnant women, lactating women, pediatric populations, or individuals with specific comorbidities have been identified for Diplacus aurantiacus extracts or its characteristic geranylflavanones. The cytotoxicity signal observed in vitro for diplacone at concentrations above 10–20 µM warrants caution in any concentrated formulation intended for systemic use.
Bush Monkey Flower (Diplacus aurantiacus / Mimulus aurantiacus) is an ecologically distinctive plant of the California chaparral with a well-documented ethnobotanical history among Miwok, Pomo, and Kumeyaay peoples for skin conditions, gastrointestinal ailments, and respiratory complaints. Its most scientifically developed aspect is the phytochemistry of its leaf resin, which has been precisely characterized and shown to consist of a series of geranylated flavanones — particularly mimulone and diplacone — that are unusual among North American medicinal plants and shared with a small number of other plant genera worldwide.
The scientific evidence for therapeutic efficacy is entirely at the preclinical stage (in vitro and one animal model). Anti-inflammatory and antiparasitic activities of isolated compounds have been demonstrated in cell culture and one rodent colitis model, and these findings are published in peer-reviewed journals. However, no human clinical trials have been conducted on any preparation or extract of D. aurantiacus for any indication. The neurological evidence is negative or mixed. Patent-level proposals for psoriasis and insect repellent applications have not been validated in controlled human studies. The Bach Flower Remedy tradition using the genus Mimulus for fear and anxiety has been tested in randomized controlled trials and found to be indistinguishable from placebo.
The notable cytotoxicity of isolated geranylflavanones at concentrations above approximately 10–20 µM in cell models represents a caution signal that argues against the casual concentration or fractionation of these compounds without further toxicological characterization.
Health conditions that Bush monkey flower may help support.
Body systems that Bush monkey flower may help support.
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