Asiatic dayflower (Commelina communis) is a widespread plant that pulls double duty as both a foraged green and a traditional herbal remedy, with modern laboratory research lending some credibility to its historical medicinal uses. Native to East Asia and now naturalized across much of North America and Europe, the plant has been eaten as a vegetable and brewed into medicinal teas for centuries. Recent studies have identified anti-inflammatory, antiviral, and blood-sugar-lowering properties in its extracts, though nearly all of this work remains preclinical.
Eating the Asiatic Dayflower
In China, Korea, and Japan, Asiatic dayflower has a long history as a wild potherb. The young leaves, stems, and flowers are all edible. The leaves and tender shoots are typically harvested before the plant flowers, when the flavor is mildest and the texture most tender. They can be eaten raw in salads, blanched and dressed with sesame oil, stir-fried, or added to soups and porridges. The taste is mild and slightly mucilaginous, somewhat like spinach with a faintly grassy note. The small blue flowers make a colorful edible garnish.
In Korean cuisine, the blanched greens (called dalgae) are sometimes served as a namul side dish, seasoned with garlic, soy sauce, and sesame seeds. In parts of China, the whole above-ground plant is dried and steeped as a cooling herbal tea, a preparation that straddles the line between food and folk medicine. Because the plant grows readily in disturbed soils, gardens, and roadsides across temperate regions, foragers in North America and Europe sometimes gather it as well. Its easy identification helps: the two large, vivid blue upper petals and one inconspicuous lower petal make it hard to confuse with anything dangerous.
Traditional Medicine Background
In traditional Chinese medicine, Asiatic dayflower (known as yā zhī cǎo) has been classified as a cooling, heat-clearing herb. Practitioners have used it for centuries to reduce fevers, relieve sore throats, ease urinary infections, and bring down swelling. In traditional Korean herbalism, similar applications appear: teas made from the dried plant are given for edema and inflammatory conditions. Japanese folk medicine, too, records the plant as a mild diuretic and fever reducer.
A comprehensive review of the Commelina genus confirmed that traditional uses across cultures span anti-diabetic, antimicrobial, analgesic, anti-inflammatory, diuretic, and even sedative applications.1Heliyon. A comprehensive review on the genus Commelina: Traditional uses, phytochemistry, and pharmacological activities That breadth of traditional use is what has drawn researchers toward the plant in recent decades. The question, of course, is how much of the folklore holds up when tested in controlled experiments.
Anti-Inflammatory Properties
One of the more compelling areas of modern research involves the plant’s effects on inflammation. A study using extracts from Commelina communis in mouse immune cells found that the extract reduced several key inflammatory signals. At higher concentrations, the extract lowered levels of nitric oxide and pro-inflammatory cytokines including TNF-alpha, IL-1 beta, and IL-6, all molecules your immune system produces during an inflammatory response.2PubMed Central. Treatment with Commelina communis Extract Exerts Anti-inflammatory Effects in Murine Macrophages via Modulation of the Nuclear Factor-κB Pathway The extract appeared to work by blocking a central inflammation pathway, reducing the activation of a protein complex called NF-kB that acts as a master switch for inflammatory gene expression.2PubMed Central. Treatment with Commelina communis Extract Exerts Anti-inflammatory Effects in Murine Macrophages via Modulation of the Nuclear Factor-κB Pathway
This matters because NF-kB is involved in a wide range of inflammatory diseases, from arthritis to cardiovascular problems. If an extract can reliably dial it down, that could theoretically have broad applications. But the work was done in cell cultures and mouse models, not in people. Anti-inflammatory effects in a petri dish do not always translate to meaningful relief when someone drinks a cup of dayflower tea. Still, identifying a plausible mechanism gives the traditional use at least a biochemical foothold.
Antiviral Activity Against Influenza
Another area where dayflower has shown promise, at least in animal studies, is fighting influenza viruses. Researchers isolated a group of alkaloids from the plant and tested them in mice infected with influenza A. Mice given these alkaloids orally for six days at varying doses had higher survival rates, lived longer on average, and carried lower viral loads in their lungs compared to untreated mice.3Archives of Virology. Anti-influenza-virus activity of total alkaloids from Commelina communis L. The protective effect was dose-dependent, meaning higher doses produced stronger results.
A separate review of plant-based antivirals against influenza A confirmed these findings and added that Commelina communis extracts also appeared to modulate the immune response in infected mice, raising levels of interferon-gamma and IL-10 while lowering TNF-alpha and IL-6.4Journal of Applied Microbiology. Plant extracts as a source of antiviral agents against influenza A virus That combination of effects suggests the plant’s compounds may help the body fight the virus while simultaneously tamping down the excessive inflammation that makes flu so dangerous.
This is genuinely interesting, but the distance between “protected mice from the flu” and “works as an antiviral in humans” is enormous. No clinical trials in people have been published. The doses used in mice do not straightforwardly convert to amounts a person could get from eating the plant or drinking a tea. For now, these results are best understood as early-stage evidence that the traditional use of dayflower for febrile illnesses was not baseless, even if the plant is nowhere close to replacing an actual antiviral medication.
Effects on Blood Sugar and Body Weight
Perhaps the most intriguing finding from a nutritional standpoint is that Asiatic dayflower contains natural compounds that interfere with how the body processes sugar. Researchers identified two potent alpha-glucosidase inhibitors in the plant: 1-deoxynojirimycin (DNJ) and a related compound called DMDP.5PubMed. Antioxidant constituents in the dayflower (Commelina communis L.) and their alpha-glucosidase-inhibitory activity Alpha-glucosidase is an enzyme in your gut that breaks complex carbohydrates down into simple sugars. When something blocks that enzyme, sugar enters the bloodstream more slowly after a meal. This is the same basic mechanism used by prescription drugs like acarbose, which are given to people with type 2 diabetes to control post-meal blood sugar spikes.
DNJ is not unique to dayflower; it is also found in mulberry leaves, which are already widely sold as a blood-sugar-support supplement in parts of Asia. But finding it in an edible wild green that people have been eating for centuries adds an interesting dimension. Nobody knows whether the concentrations present in a serving of blanched dayflower greens would be enough to meaningfully blunt a blood sugar spike, but the compounds are demonstrably there.
On the weight management side, an animal study using dried Commelina communis tea in mice fed a high-fat diet found that the extract had anti-obesity effects and slightly improved insulin sensitivity. The researchers zeroed in on glucoluteolin, a flavonoid abundant in the plant, and showed that it reduced fat accumulation in fat cells and decreased glucose uptake by those cells.6Journal of Functional Foods. Anti-obesity effects of Asian dayflower, Commelina communis, in mice with high-fat diet-induced obesity and in 3T3-L1 cells In other words, the flavonoid seemed to make fat cells less enthusiastic about storing energy. Again, this is in mice and in isolated cells, not in people on a diet. But the overlap between the anti-diabetic and anti-obesity findings paints a picture of a plant whose chemical makeup is genuinely oriented toward metabolic effects.
What Makes the Plant Bioactive
The pharmacological activity of Asiatic dayflower comes from an unusually diverse chemical profile for a common weed. Phytochemical analysis has identified alkaloids, flavonoids, phenolic acids, tannins, glycosides, lignans, and polyols in the plant’s above-ground parts.1Heliyon. A comprehensive review on the genus Commelina: Traditional uses, phytochemistry, and pharmacological activities That is a wider spread of bioactive compound classes than you would find in most salad greens.
On the antioxidant side, researchers identified eleven distinct flavonoid glycosides in the aerial parts of the plant, including orientin, vitexin, isovitexin, isoorientin, swertisin, and flavocommelin.5PubMed. Antioxidant constituents in the dayflower (Commelina communis L.) and their alpha-glucosidase-inhibitory activity Several of these flavonoids are also found in well-studied foods like passionflower, bamboo leaves, and various medicinal herbs. Glucoluteolin, the flavonoid linked to the anti-obesity effects described above, doubles as an antioxidant. So the same compounds appear to be pulling multiple levers at once: reducing oxidative stress, curbing inflammation, and interfering with sugar and fat metabolism.
The alkaloid fraction, meanwhile, is what showed the strongest antiviral activity. Alkaloids are nitrogen-containing compounds that plants often produce as chemical defenses against herbivores and pathogens. In dayflower, this defense chemistry happens to interact with mammalian immune pathways in ways that turned out to be useful, at least in laboratory and animal settings.
Safety and Foraging Considerations
Asiatic dayflower has been eaten without apparent harm across East Asia for centuries, and no reports of toxicity from consuming the plant in normal food quantities have surfaced in the scientific literature. The comprehensive review of the Commelina genus did not flag significant toxicity concerns at dietary levels.1Heliyon. A comprehensive review on the genus Commelina: Traditional uses, phytochemistry, and pharmacological activities That said, no formal safety studies (the kind with defined maximum tolerated doses in humans) have been conducted specifically on Commelina communis. The safety case rests on a long history of traditional use rather than on clinical data.
For foragers, the bigger concern is where the plant was growing rather than what the plant itself contains. Wild edible plants harvested near roads, agricultural fields, or industrial areas can accumulate heavy metals like lead and cadmium from contaminated soil. Research on other foraged wild plants and flowers has found that heavy metal contamination varies widely depending on location, and some samples exceeded recommended limits.7PubMed Central. Chemical and microbial risk assessment of wild edible plants and flowers Dayflower, which thrives in disturbed and sometimes degraded habitats, would be particularly susceptible to this problem. If you plan to forage it, stick to areas well away from road runoff, treated lawns, and places where pesticides or herbicides have been applied.
People taking diabetes medication should also exercise caution. Because the plant contains natural alpha-glucosidase inhibitors, consuming large quantities alongside drugs that lower blood sugar could theoretically amplify the effect and cause blood sugar to drop too low. This is speculative rather than documented, but it follows logically from the plant’s chemistry, and it is the kind of interaction that rarely gets studied in wild food plants.
The Gap Between Lab Findings and Real-World Use
One honest assessment of dayflower research is that it sits in a frustrating middle zone: too promising to dismiss, too preliminary to recommend. Every significant pharmacological finding so far comes from cell culture experiments or mouse models. No randomized controlled trials in humans have tested whether drinking dayflower tea reduces inflammation, fights off the flu, or lowers blood sugar. This is not unusual for a traditional medicinal plant. The vast majority of the world’s medicinal herbs have never been subjected to clinical trials, partly because they cannot be patented and there is little financial incentive to fund expensive human studies.
What is encouraging is the consistency of the results across different research groups and different biological targets. The anti-inflammatory findings align with the traditional use for fever and swelling. The alpha-glucosidase inhibition aligns with the folk practice of using dayflower tea around meals. The antiviral data aligns with the traditional use for colds and febrile illness. When multiple independent lines of lab evidence point in the same direction as centuries of traditional use, it is reasonable to take the plant more seriously than a random weed, even without human clinical data.
For anyone interested in incorporating dayflower into their diet, treating it as you would any other foraged green is sensible: eat moderate amounts, source it from clean environments, and do not rely on it as a substitute for medical treatment. As a nutritious wild vegetable with an interesting chemical profile, it earns its place on the plate. As a medicine, the jury is still out.
The Famous Blue Pigment
Beyond food and medicine, Asiatic dayflower has a long and somewhat surprising history in the arts. The vivid blue pigment in its petals, known as commelinin, is a metalloanthocyanin complex that produces one of the truest blues found in nature. In Japan, the plant (called tsuyukusa) was historically cultivated specifically for its flower pigment, which was used to create preliminary sketches on fabric for yuzen-dyed kimono. The pigment washes out cleanly with water, making it ideal as a temporary guide that leaves no trace once the permanent dyes are applied.
A specially cultivated large-flowered variety called aobana was grown in Shiga Prefecture specifically for pigment production. The petals were pressed onto paper to create aobana-gami, sheets of concentrated blue dye that could be reconstituted with water as needed. This same fugitive blue was used by woodblock print artists as a preliminary layout color. The pigment’s water-solubility, which makes it useless as a permanent paint, is precisely what made it invaluable as a disappearing guide line.
Modern materials science has taken notice of commelinin for different reasons. The complex is unusually stable for a plant pigment at neutral pH, and its structure, involving multiple anthocyanin and flavone molecules coordinated around metal ions, has been studied as a model for how nature achieves intense color without synthetic chemistry. Researchers interested in natural food colorants have examined it as a potential replacement for synthetic blue dyes, though commercial production remains impractical given the tiny amount of pigment each flower produces. For the home forager, though, the petals make a striking and entirely edible blue garnish that briefly turns drinks and dishes an improbable shade of sky blue before fading, a small, beautiful reminder that this common roadside weed has been useful to humans in more ways than most people realize.