Southeast Asia

Rice Paddy Herb / Rau Om

Limnophila aromatica.

Leaf and stem.

Part Used

Fresh, always – should never be cooked, only added raw or very briefly at the end.

Form

Local / Regional Names

Rau om, ngò om (Vietnamese); phak kayang (Thai) – also called 'sweet cumin' or 'Vietnamese watercress' in some English sources despite being neither a cumin relative nor a watercress.

Countries / Cuisines

Vietnam (especially southern), Thailand, Cambodia.

Flavor & Aroma

Citrusy, cumin-and-dill-adjacent, quite distinctive; identifiable stems have fine hairs and a hollow, slightly squishy texture.

Culinary Uses

Finishing herb for sour soups and noodle dishes.

Classic Dishes

Canh chua (Vietnamese sour soup); fish-based noodle soups.

Pairings

Tamarind, fish, sour broths.

Timing

Add finely chopped only at the very end of cooking or at the table – heat quickly destroys its distinctive flavor.

Storage

Fresh keeps only a few days refrigerated; an aquatic plant that wilts quickly out of water.

Substitutions

No close substitute for its unusual citrus-cumin-dill flavor combination.

Cultural / History Notes

An aquatic herb traditionally grown directly in flooded rice paddies, giving it its English common name – one of the more botanically unusual growing habits among the herbs in this entire reference.

Blend Cross-References

Not a blend component; used fresh.