Thettran, nirmali in Hindi and kataka in Sanskrit, is the clearing-nut tree. Its seeds have been rubbed inside water pots for centuries in South India to make muddy water settle and turn clear. Modern studies confirm that the seeds act as a natural coagulant. It is a relative of nux vomica, Strychnos nux-vomica, but its seeds contain far less strychnine.
- Botanical name
- Strychnos potatorum L.f.
- Family
- Loganiaceae
- Tamil
- Thettran
- Hindi
- Nirmali
- Sanskrit
- Kataka
- Parts used
- Seed
- Habit
- Dry-country tree whose seed settles muddy water
- Last updated
- 2026-10-27
How to recognise Thettran
It is a medium-sized deciduous tree with dark, rough bark.
The leaves are glossy, oval and opposite, with three to five veins from the base.
Small, greenish-white flowers grow in clusters in the leaf axils.
The fruits are round, shiny berries that turn black, each with one seed.
The seed is round, flattened and covered in fine silky hairs.
Traditional use of Thettran
Household
A seed is rubbed on the inside of a clay pot of muddy water, which then clears in an hour or two as the mud settles.
South Indian household practice
Ayurveda
Kataka seed is used in Ayurvedic eye preparations.
Ayurvedic practice
Modern notes on Thettran
The seeds contain polysaccharides and proteins that bind fine clay particles so they clump and sink.
Researchers have tested clearing-nut seed as a low-cost water treatment in villages.
Settling clears water but does not kill germs; water still needs boiling or other disinfection.
Thettran safety
Boil or disinfect water after clearing it with the seed. Do not eat the seeds or fruit.
Ecology and sourcing
It grows in dry deciduous forests of India, Sri Lanka and Myanmar.
Birds and monkeys eat the fruit pulp.
It tolerates drought.
Related plants
Questions about Thettran
How does the seed clear water?
It makes fine mud particles clump and settle.
Does Thettran make water safe?
No. Water still needs boiling.
Is Thettran poisonous like nux vomica?
It has far less strychnine, but do not eat it.
What is nirmali?
Its Hindi name, meaning clean.
Where does Thettran grow?
In dry forests of South Asia.
Sources
- Strychnos potatorum L.f. — Plants of the World Online, Kew (search) (accessed 2026)
- Wikidata item Q3595916 (Strychnos potatorum)
Educational page about a plant. It is not medical advice, not a diagnosis, and not an offer to sell. Traditional use is historical. If you need care, ask a licensed clinician. Questions: hello@meevamed.com.