# Wood sorrel (Oxalis acetosella)

**Oxalis*; Irish *seamsóg**

**Known today as.** *Oxalis acetosella*. A delicate woodland plant with clover-like, sour-tasting leaves of three leaflets and white, veined flowers.

Kind: Plant  
Poisoning: Oxalate poisoning (https://thethinkingpress.org/materia-medica/poisons/oxalate)

> **Caution.** Contains oxalic acid; avoid in quantity, especially with a history of kidney stones.

## What was it used for?

The leaves eaten fresh or made into a cooling drink for their sharp, lemony taste, and used as a folk remedy for fevers and scurvy.

## What does modern science say?

Its sharp taste comes from oxalic acid, mildly toxic in quantity and best avoided by those prone to kidney stones.

## Pharmacognosy and toxicology

- **oxalic acid and potassium oxalate**: the sour, up to 1 per cent fresh
- **vitamin C**: 
- **flavonoids**: 

**Mechanism.** The lemon taste is oxalate, which cools in the Galenic sense and binds calcium in the kidney in quantity; the vitamin C was the scurvy use. Salt of sorrel (potassium hydrogen oxalate), once extracted from it, was the stain remover and a poison of the nineteenth century.

**Dose.** A few leaves are safe; sheep and children eating it in quantity have had oxalate poisoning.

**Standing.** A wild food; no monograph.

## What lore surrounds it?

Wood sorrel is one of the leading candidates, with young clover, for the true shamrock with which St. Patrick is said to have explained the Trinity, a legend first recorded only in 1726, more than a thousand years after his lifetime, and absent from earlier English accounts of the Irish shamrock custom. The confusion may go back to English writers mishearing the Irish *seamsóg*, wood sorrel, as *seamróg*, young clover. Surveys of what the Irish actually call shamrock have never settled the question, with lesser and white clover far outnumbering wood sorrel among modern answers.

## What did the older authorities say?

**Pliny.** Pliny's whole account of the oxys fits in a sentence: “The oxys is a plant with three leaves; it is given for derangement of the stomach, and patients eat it who are suffering from intestinal hernia.”

**Culpeper.** Venus owns it; it serves all the purposes of the other sorrels and is more effectual against putrefaction of the blood and ulcers of the mouth, to quench thirst and stay vomiting; its juice turns red when clarified “and makes a most dainty clear syrup”; gargled, it helps “a foul stinking canker.”

## Sources

- Wikipedia, “Shamrock.”
- Pliny the Elder, *Natural History* 27.89, trans. J. Bostock & H. T. Riley (1855), Perseus Digital Library.
- Culpeper, N. (1653). *The Complete Herbal*, “Wood Sorrel.” Project Gutenberg #49513.
- Frohne, D., and Pfänder, H. J. (2005). *Poisonous Plants*, 2nd ed., “Oxalidaceae.”

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*Wood sorrel.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-01. The Thinking Press. https://thethinkingpress.org/materia-medica/wood-sorrel

Historical description, not medical advice.