The Verdict: Common Knotgrass is Edible
Yes, the common knotgrass (Polygonum aviculare) is considered edible and has been consumed by humans for centuries. It is a versatile wild plant with a nutritional profile that includes flavonoids, tannins, phenolic acids, and vitamin C, among other compounds. The aerial parts, including the young shoots and leaves, are the most commonly eaten, often added to salads, soups, stews, or made into a tea.
Historically, remnants of knotgrass seeds have been found in the stomach of the Tollund Man, a bog body from Denmark dating back over 2,400 years, offering concrete evidence of its historical use as a food source. In certain parts of the world, like Turkey and along the Turkish-Georgian border, it continues to be prepared as a food, typically boiled, stewed, or roasted.
How to Safely Identify Common Knotgrass
Proper identification is the most critical step when foraging for any wild plant. Knotgrass can be confused with other plants, so knowing its specific features is paramount. Common knotgrass is not an actual grass but is related to buckwheat.
Key Identification Features:
- Growth Habit: It is a low-growing, sprawling annual herb with wiry, sprawling stems that can form dense mats. Stems typically grow close to the ground, reaching up to 60 cm in length.
- Stems: The stems feature distinctive swollen joints or 'knots' where leaves and side branches emerge, giving the plant its name. These stems are round in cross-section.
- Leaves: The leaves are small, narrow, and lance-shaped, arranged alternately along the stem. They are often bluish-green and fall off easily from the main stems, especially as the plant matures.
- Ochrea: At the base of each leaf, there is a prominent, thin, papery sheath called an ochrea that surrounds the stem. This is a key feature of the Polygonaceae family.
- Flowers: The flowers are tiny, greenish-white or pinkish, and often appear in small clusters at the leaf axils from May to October.
Before consuming any foraged plant, it is essential to be 100% certain of its identity. Use multiple reliable field guides and resources. If in doubt, do not eat it.
Potential Health Benefits and Risks
Historically, knotgrass has been utilized in traditional herbal medicine for various conditions, which can be attributed to its chemical composition.
Potential Benefits:
- Diuretic Properties: Flavonoid glycosides in knotgrass are believed to have a diuretic effect, helping to increase urine production and flush the urinary tract.
- Astringent Effects: The plant's tannin content gives it astringent properties, which has led to its traditional use for ailments like diarrhea and mouth inflammation.
- Antioxidant Activity: Knotgrass contains several compounds with antioxidant properties, such as flavonoids and phenolics, which help protect cells from oxidative stress.
Risks and Precautions:
- Oxalic Acid: Knotgrass, like many leafy greens and other plants in its family (e.g., dock and rhubarb), contains oxalic acid. Consuming large quantities could potentially lead to kidney issues, especially for those prone to kidney stones or with existing kidney problems. Cooking can help reduce the oxalic acid content.
- Digestive Issues: Excessive consumption may cause mild side effects like digestive upset or diarrhea.
- Herbicide Contamination: Avoid foraging for knotgrass from areas that might have been sprayed with herbicides, such as roadsides, sidewalks, or agricultural fields.
- Vulnerable Populations: Pregnant women, breastfeeding mothers, and individuals with liver or kidney issues should consult a healthcare provider before consuming knotgrass.
Culinary Uses: How to Prepare Knotgrass
Foragers typically harvest the young, fresh shoots and leaves, as they are the most tender and palatable. The flavor is often described as mild and slightly tangy. Here are a few ways to prepare it:
- Raw in Salads: Young, tender leaves can be added directly to fresh salads for a nutritional boost.
- Cooked in Soups and Stews: The leaves and shoots can be boiled or stewed, similar to spinach or other greens. In Turkish cuisine, it is stewed with bulgur or rice.
- Herbal Tea: Dried knotgrass can be steeped in hot water to create a healthful tea. The European Medicines Agency notes its long-standing use for common cold and urinary tract symptoms.
- Pickled: In certain regions, knotgrass is pickled as a traditional food.
Knotgrass vs. Japanese Knotweed: A Critical Distinction
A common and dangerous mistake is confusing common knotgrass (Polygonum aviculare) with Japanese knotweed (Reynoutria japonica), a highly invasive and different species. Although Japanese knotweed is also edible, its identification is much more complex and often grows in areas that may have been treated with herbicides.
| Feature | Common Knotgrass (P. aviculare) | Japanese Knotweed (R. japonica) |
|---|---|---|
| Growth Habit | Low-growing, sprawling, mat-forming annual | Upright, tall, bamboo-like perennial |
| Stems | Thin and wiry with conspicuous knots | Thick, hollow, and red-speckled, resembling bamboo |
| Leaves | Small, narrow, lance-shaped | Large, broad, and spade-shaped (6+ inches long) |
| Flowers | Tiny, greenish-white or pinkish, in small clusters | Showy, lacy white flower clusters in late summer |
| Root System | Deep taproot but less aggressively spreading | Rapidly spreading, destructive root system (rhizomes) |
It is imperative to know the difference. The invasive nature of Japanese knotweed also means that foraging in public areas can sometimes be legally restricted.
Foraging Ethically and Safely
Responsible foraging practices are essential. Ensure you have a positive identification and harvest from clean, uncontaminated areas. Never take more than you need, and leave plenty of the plant behind to ensure its continued growth.
For those interested in learning more about the bioactive compounds found in knotgrass, the National Institutes of Health (NIH) offers detailed scientific research on its medicinal properties.
Conclusion
Common knotgrass is a safe and edible wild plant with a rich history of culinary and medicinal use. Its leaves and young shoots can be enjoyed in various dishes, adding a mild, tangy flavor. However, successful and safe foraging depends on confident identification, understanding potential health risks associated with large quantities, and sourcing from uncontaminated areas. Always prioritize safety and exercise caution when introducing any new wild food into your diet.
