What acid is present in Oxalis?

January 8, 2026 •

3 min read

The distinctive, tart flavor of plants in the Oxalis genus, commonly known as wood sorrel, comes from a specific natural compound. The key to this sour taste is a dicarboxylic acid called oxalic acid.

Quick Summary

The genus Oxalis contains oxalic acid, the compound responsible for its signature sour flavor. The text details the nature of oxalic acid, its roles in plants, potential health effects, and occurrence in other foods.

Key Points

Oxalic Acid is the Source: The sour taste of Oxalis plants is due to the presence of oxalic acid, from which the genus's name is derived.
Oxalate Salts are Formed: Oxalic acid can bind with minerals like calcium to form crystalline oxalate salts, which can cause irritation if consumed in large quantities.
Many Foods Contain Oxalates: High concentrations of oxalates are also found in many common and healthy foods, including spinach, rhubarb, and beets.
Toxicity is Dose-Dependent: Serious health issues from oxalate toxicity are rare for healthy individuals and typically only occur with large, excessive consumption.
Mitigation with Preparation: Boiling high-oxalate plants and pairing them with calcium-rich foods can significantly reduce the amount of oxalate absorbed by the body.
Risk for Sensitive Individuals: People with a history of kidney stones should exercise caution and may need to follow a low-oxalate diet, as advised by a healthcare professional.

The Sour Secret of Oxalis

Plants of the Oxalis genus, including wood sorrel, get their characteristic sour or tangy taste from a compound called oxalic acid. This organic acid was first isolated from wood sorrel plants, which is how it earned its name. In nature, oxalic acid is often found bound to minerals, particularly calcium, forming crystalline salts known as oxalates. The concentration of this compound varies by species, plant part, and growing conditions, with leaves generally having the highest levels.

The Dual Role of Oxalic Acid in Plants

While oxalic acid is responsible for the refreshing, tart taste enjoyed by foragers in small quantities, it plays a much more complex role in the plant's biology. It is not merely a waste product but serves several key functions vital for the plant's survival and growth.

Calcium Regulation: Plants use oxalic acid to manage and detoxify excess calcium within their cells. By binding to calcium and forming insoluble calcium oxalate crystals (raphides), the plant can safely sequester this mineral, preventing cellular toxicity.
Defense Mechanism: The formation of calcium oxalate crystals acts as a natural deterrent against herbivores. The needle-like crystals in the plant's tissues can cause irritation and inflammation in the mouths and throats of animals that try to eat it.
Heavy Metal Detoxification: Oxalic acid can chelate heavy metal ions in the soil, helping the plant to tolerate and thrive in otherwise toxic soil environments.
Ion Balance: It helps maintain the overall balance of ions within the plant's tissues, particularly when dealing with an excess of inorganic cations.

Comparison of Oxalic Acid Content

It is a common misconception that Oxalis is exceptionally high in oxalates compared to all other foods. In fact, many common and healthy vegetables contain significant amounts. The table below compares the approximate oxalate content of several foods, demonstrating that Oxalis is not an outlier.


Food Item	Soluble Oxalate (mg/100g)	Total Oxalate (mg/100g)	Notes
*Wood Sorrel (Oxalis) leaves*	42-125	273-954	Levels vary significantly with size and growing conditions.
Spinach	65-130	650-1300	Oxalate content in fresh weight.
Rhubarb	-	~500	Leaves are particularly high and toxic.
Beet Greens	-	~610	Higher in greens than in the root.
Swiss Chard	-	~960	Contains substantial levels.
Broccoli	-	~190	Considered a moderate source.

The Impact of Oxalic Acid on Human Health

For the vast majority of healthy people, eating a normal amount of oxalate-containing foods, including wood sorrel, poses no significant health risk. The potential problems arise when large quantities are ingested, or in individuals with predispositions to certain medical conditions, most notably kidney stones.

Excessive intake of oxalic acid can be toxic because it binds to calcium in the body, which can cause an acute and dangerous drop in blood calcium (hypocalcemia). The resulting calcium oxalate can form crystals that, when excreted by the kidneys, can lead to the formation of kidney stones and, in severe cases, renal failure. For those at risk, health professionals may recommend a low-oxalate diet to reduce urinary oxalate levels.

Mitigating Oxalate Intake with Cooking

For foragers and home cooks, simple food preparation techniques can help reduce the soluble oxalate content of high-oxalate foods like wood sorrel. Boiling vegetables can remove a significant portion of the soluble oxalates, as they leach into the cooking water. Discarding the water is key to this process. Additionally, pairing high-oxalate foods with calcium-rich foods (like cheese in a pesto or dairy in a soup) can bind the oxalates in the digestive tract, preventing them from being absorbed into the bloodstream. For example, a sorrel soup with a dollop of sour cream or a sorrel pesto with parmesan cheese can effectively lower the amount of bioavailable oxalate.

Conclusion

In conclusion, the acid present in Oxalis is oxalic acid, a compound responsible for its signature sour taste. While oxalic acid plays crucial roles in the plant's biology, its consumption by humans requires moderation due to its potential health effects, particularly for those prone to kidney stones. However, by using simple cooking methods and pairings, most individuals can safely enjoy the unique flavor of wood sorrel and other high-oxalate foods without risk. As with any wild food, moderation and proper preparation are key to a safe and enjoyable experience.

For more detailed information on plant chemistry, a great resource can be found on Wikipedia's page for oxalic acid, which discusses its chemical properties and biological role.

Frequently Asked Questions

The primary acid responsible for the tart flavor of wood sorrel, which belongs to the Oxalis genus, is oxalic acid.

While Oxalis contains oxalic acid, it is only considered toxic to humans if ingested in very large quantities. For most healthy people, consuming moderate amounts is not dangerous, but excessive intake is not recommended.

All parts of the Oxalis plant are toxic to pets, including dogs, cats, and horses, because the soluble oxalates can cause a dangerous drop in blood calcium. Symptoms can include drooling, vomiting, and lethargy.

To reduce the amount of absorbable oxalate, boil the leaves and discard the cooking water. You can also combine the sorrel with calcium-rich foods, such as cheese or sour cream, which helps bind the oxalates.

Yes, for individuals who are sensitive or prone to kidney stones, high dietary oxalate intake can contribute to the formation of calcium oxalate crystals in the urinary tract. A high intake is not a risk for the majority of the population.

Wood sorrel has a higher concentration of oxalic acid than spinach. However, the quantities typically foraged and consumed are much smaller than a typical serving of spinach, making the overall risk for a healthy person very low.

Oxalic acid is the organic acid itself. Oxalate is the salt form that is created when oxalic acid binds to minerals, such as calcium. In nutritional science, the terms are often used interchangeably.