# Sundew (Drosera rotundifolia)

*Round-leaved sundew, dew plant, red rot, youth-wort, *Rosa Solis*; *Herba rosellae*, *Sonnenthau rosollis*, *Rosée du Soleil*; *Drosera rotundifolia* L.*

**Known today as.** *Drosera rotundifolia*, of the family Droseraceae, a small insectivorous perennial of peaty bogs and the muddy edges of ponds and rivers. Its round leaves lie flat on the ground, covered with long red sticky hairs, each tipped with a gland whose fluid “looks like a dewdrop, hence its name,” Grieve writes. The hairs curve slowly inward on any insect that alights, and the glands then secrete a fluid that digests it. The small white flowers open only in sunshine. The flowering plant, dried in the air, is the drug.

Kind: Plant

> **Caution.** Culpeper records that the leaves raise blisters on the skin, and Grieve calls the juice acrid and caustic. None of the sources read for this entry reports on its safety when taken.

## What was it used for?

A remedy for coughs and the lungs. Culpeper held its distilled water in wine good for consumption and “all other diseases of the lungs, as phthisicks, wheezings, shortness of breath, or the cough.” Grieve records it as used with advantage in whooping cough, early consumption, chronic bronchitis, and asthma; she adds that the juice was said to take away corns and warts and could curdle milk.

## What does modern science say?

No European monograph for it was found for this entry. A 2022 laboratory study, noting that sundew extracts are traditionally used for cough during a common cold, found that an extract and its flavonoids relaxed the airway muscle of mouse tracheal slices and increased the beating of their cilia; it was not a study in people, and the searches of Europe PMC made for this entry found no clinical trial of sundew alone.

## Pharmacognosy and toxicology

- **quercetin**: a flavonoid that, in a 2022 laboratory study, raised the beating of the airway cilia
- **hyperoside**: with 2 -O-galloylhyperoside, among the flavonoids that relaxed airway muscle
- **citric acid**: with malic acid, in the juice, by Grieve’s account

**Mechanism.** In mouse tracheal slices an extract relaxed the airway muscle and quickened the cilia; quercetin and 2 -O-galloylhyperoside inhibited the enzymes PDE1A and PDE4D. Not a study in people.

**Standing.** There is no European monograph, and no clinical trial of sundew alone was found for this entry.

## What lore surrounds it?

Grieve reports that in America it had been advocated as a cure for old age.

## What did the older authorities say?

**Culpeper, *The Complete Herbal* (1653).** Culpeper puts it under the Sun and the sign Cancer, and observes that its leaves are moist even on the hottest day: “the hotter the sun shines on them, the moister they are.” The leaves laid on the skin raise blisters, “which has caused some to think it dangerous to be taken inwardly,” but he answered that other things which draw blisters are not dangerous to take, and noted a common drink of it with aqua vitae and spices, used for qualms and passions of the heart.

## Sources

- Grieve, M. *A Modern Herbal*, “Sundew.” As published on botanical.com.
- Culpeper, N. *The Complete Herbal*, “ROSA SOLIS, OR SUN DEW.” Project Gutenberg, 49513.
- Hake A, et al. (2022). Effects of Extracts and Flavonoids from <i>Drosera rotundifolia</i> L. on Ciliary Beat Frequency and Murine Airway Smooth Muscle. *Molecules (Basel, Switzerland)*. PMID 36235159.
- Grieve, M. *A Modern Herbal*, “Sundew.” As published on botanical.com.
- Hake A, et al. (2022). Effects of Extracts and Flavonoids from <i>Drosera rotundifolia</i> L. on Ciliary Beat Frequency and Murine Airway Smooth Muscle. *Molecules (Basel, Switzerland)*. PMID 36235159.

---

*Sundew.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-17. The Thinking Press. https://thethinkingpress.org/materia-medica/sundew

Historical description, not medical advice.