Understanding Oxalate in Oxalis Species
Oxalis, commonly known as wood sorrel or sourgrass, is a widespread genus of plants. Its characteristic sour, tangy flavor is due to the presence of oxalic acid and other soluble oxalate salts. While a small amount provides a pleasant, lemony flavor for culinary use, large quantities can be toxic. The concentration of oxalates varies significantly among different species and even within the same plant depending on factors like maturity and growing conditions.
Oxalic Acid vs. Oxalate
It's important to understand the difference between oxalic acid and oxalate. Oxalic acid is the organic acid that gives the plant its tart taste. In plants, it exists in both soluble and insoluble forms. Soluble oxalates, when ingested, bind to calcium in the body, which can interfere with calcium absorption and potentially form calcium oxalate crystals that lead to health problems. Insoluble oxalates are typically less bioavailable but can still be problematic.
Oxalate Levels in Specific Oxalis Species
Different Oxalis species contain varying concentrations of oxalates. Here are a few examples:
- Oxalis corniculata (Yellow wood sorrel): The leaves of this common garden weed can contain between 7% and 12% oxalate on a dry weight basis. While the leaves are edible, this relatively high concentration means they should only be consumed in moderation.
- Oxalis tuberosa (Oca or New Zealand yam): A study found that the tubers of this species had oxalate levels ranging from 80 to 194 mg/100 g wet matter in raw form. The same study also found that baking the tubers significantly increased the oxalate content, a result that surprised researchers.
- Oxalis pes-caprae (African wood-sorrel): This invasive species, toxic to livestock, contains high concentrations of oxalic acid, especially in its flower scapes. Its high oxalate content makes it a significant risk for grazing animals.
Comparing Oxalate Levels: Oxalis vs. Common Foods
To put the oxalate levels in Oxalis into perspective, it helps to compare them to other foods known for their high oxalate content. As seen in the table below, some species of Oxalis can have comparable or even higher oxalate concentrations than more commonly recognized high-oxalate foods like spinach and rhubarb.
| Food Item | Typical Oxalate Content (mg/100g) | Notes |
|---|---|---|
| Oxalis corniculata leaves | 7,000–12,000 (dry weight) | Significantly higher on a dry weight basis |
| Oxalis tuberosa (oca) tubers | 80–194 (raw wet weight) | Baking can increase concentration |
| Spinach | ~800 | A well-known high-oxalate food |
| Rhubarb leaves | ~500 | Extremely high and considered toxic |
| Beets | ~300–400 | A common source of dietary oxalate |
| Sweet Potatoes | ~100–200 | Contains moderate to high levels of oxalates |
Health Risks of Excessive Oxalate Intake
For most healthy individuals, moderate consumption of Oxalis as a garnish or flavor enhancer poses little risk. However, ingesting large quantities, especially over a prolonged period, can have serious health consequences. The main risks include:
- Kidney Stone Formation: The binding of soluble oxalates with calcium in the body can lead to the formation of calcium oxalate crystals, a primary component of kidney stones. This risk is particularly high for individuals with a history of kidney issues or hyperoxaluria.
- Mineral Deficiency: High oxalate intake can bind up the body's calcium supply, potentially leading to nutritional deficiencies if not managed.
- Gastrointestinal Distress: Excessive consumption can irritate the stomach and intestines, leading to symptoms like nausea, vomiting, and diarrhea.
- Organ Damage: In severe cases of poisoning, the formation of oxalate crystals can damage the kidneys, blood vessels, heart, and lungs, especially in vulnerable populations like pets and young children.
Safety Precautions for Humans and Pets
While wood sorrel is an appealing edible wild plant, caution is necessary, particularly for those with existing health conditions. People with rheumatism, arthritis, gout, or a history of kidney stones should avoid consuming Oxalis. Cooking the leaves can help reduce the amount of oxalic acid.
Pet owners should be particularly vigilant. All parts of the Oxalis plant are considered toxic to cats and dogs. The bitter taste may deter animals from eating large amounts, but even small quantities can be dangerous and cause symptoms such as drooling, vomiting, diarrhea, tremors, and in severe cases, kidney failure. If you have pets, it is best to avoid keeping Oxalis plants in areas they can access.
Conclusion
Oxalis contains significant levels of oxalate, a compound that gives it a sour taste but can be harmful if consumed in large quantities. The amount of oxalate varies by species, with some wild varieties like yellow wood sorrel and oca having notable concentrations. While most healthy individuals can safely enjoy small amounts of Oxalis leaves as a culinary garnish, those with pre-existing health conditions should be cautious or avoid it entirely. The risk to pets is more acute, and pet owners should prevent their animals from ingesting any part of the plant. As with any wild food, moderation is key, and understanding the potential risks is essential for responsible foraging and gardening. For further information on safe wild plant consumption, consider consulting expert resources like the ForageSF blog.
Frequently Asked Questions
Is it safe to eat Oxalis leaves?
For most healthy adults, consuming small quantities of Oxalis leaves occasionally, such as in a salad, is safe. However, due to its high oxalate content, large or frequent consumption should be avoided. People prone to kidney stones, gout, or arthritis should not eat it at all.
Can my pet get sick from eating Oxalis?
Yes, Oxalis is toxic to both cats and dogs. Ingestion can lead to a sudden drop in calcium and cause symptoms such as drooling, vomiting, diarrhea, lethargy, and tremors. In severe cases, it can cause kidney damage.
Does cooking Oxalis reduce its oxalate content?
Yes, cooking Oxalis leaves can reduce their oxalic acid content. For instance, studies on the related food oca show that boiling and steaming reduce oxalate levels, while baking can increase them.
How does Oxalis taste?
Oxalis has a distinctively sour, lemony, and tangy flavor, which is why it is also known as sourgrass or wood sorrel. This taste is due to the oxalic acid present in its leaves.
Which part of the Oxalis plant contains oxalates?
All parts of the Oxalis plant contain oxalate, though the concentration can vary. The leaves and flower scapes are particularly high in oxalic acid.
What are the symptoms of oxalate poisoning from Oxalis?
Symptoms of mild oxalate poisoning in humans can include nausea, stomach irritation, and diarrhea. Severe poisoning can cause more serious issues, such as kidney damage and nutrient deficiencies. Symptoms in pets include drooling, vomiting, diarrhea, and potential kidney failure.
How does oxalate affect the body?
Once ingested, soluble oxalates bind with calcium in the bloodstream. This can lead to decreased calcium absorption and the formation of calcium oxalate crystals, which can accumulate in the kidneys and other organs.
