Rice paddy herb
Also known as ngo om, ngò om, rau om, phak khayaeng, Limnophila aromatica
Quick answer
A small semi-aquatic herb that grows in flooded rice fields and tastes of citrus and cumin at once. It is the herb that makes a southern Vietnamese canh chua taste like itself, and almost nothing else stands in for it.
- Tastes of
- citric, cumin-like, green, floral
- Heat
- Scoville does not apply
- Goes with
- White fish, Tomato
- If you have none
- Coriander leaf — see the limits
Other names
What this spice is called elsewhere, and where the translation is not clean.
ngò om
Vietnamese — Southern Vietnam
Ngò is also the southern word for coriander, so ngò om, ngò gai (culantro) and ngò rí (coriander leaf) are three different plants that a quick translation will run together. In the north the herb is rau om.
phak khayaengผักแขยง
Thai
ma om
Khmer
Flavour and aroma
Lemony and fresh at first, with a cumin-like warmth behind it and a slight bitterness if eaten in quantity raw.
Citrus and cumin together — lemony, with a warm, faintly musky undertone that most people first read as cumin. The combination is unlike any other herb in common use.
Bright green, the stems pale and succulent.
Soft and succulent; stems and leaves are both eaten, chopped.
Heat
Pungency scale: none — this spice is not pungent
No heat.
- Limonene — The citrus top note, and the constituent most analyses find in the largest amount.(what limonene is)
- Perillaldehyde — A spicy, cumin-adjacent aldehyde that goes some way to explaining why the herb reads as citrus and cumin together.
Published analyses disagree considerably, with some samples dominated by ocimene or terpinolene instead. The composition appears to vary with origin and growing conditions, and the figures here describe the commonest finding rather than a fixed profile.
Pairings
Ranked by how well established the combination is, with the reason and the caveats attached.
Foods
White fish
ClassicCanh chua cá, the sour fish soup of the Mekong Delta, is finished with ngò om; its citrus-and-cumin smell is the top note over the fish, tamarind and pineapple. Freshwater catfish and snakehead are the usual fish.
How: Chopped and stirred into the finished soup off the heat
Tomato
StrongTomato is a constant of canh chua and of the southern Vietnamese sour soups the herb belongs to.
Other spices and blends
If you have no rice paddy herb
What to use instead, and — more usefully — where each replacement stops working.
Coriander leaf with Cumin
PoorCoriander leaf with a squeeze of lemon and the smallest pinch of ground cumin gestures at the citrus-and-cumin smell. It is a sketch rather than a stand-in: none of the three carries the herb’s own floral lemon quality.
| Flavour | Aroma | Colour | Heat |
|---|---|---|---|
| partial | partial | close | similar |
Works for
- A sour fish soup where the herb would be one of several garnishes
Does not work for
- Canh chua made to a southern Vietnamese standard, where ngò om is the identifying finish
- Eating raw from a herb plate
- Any dish where cumin would be a noticeable, unwelcome addition
Cuisine: The soup will be good and will not taste of the Mekong Delta; better to leave the herb out and say so than to pretend.
There is no real substitute. The combination is recorded because people ask, and because the honest answer — that it does not arrive — is more useful than silence.
Preparation and use
Chop stems and leaves together and stir into the finished soup off the heat, or put the sprigs on the herb plate. There is no good substitute: a little coriander leaf with a squeeze of lemon and a pinch of ground cumin points in the right direction and does not arrive.
A finishing herb for sour soups and fish: canh chua above all, sour fish curries in the Mekong Delta, and Isan fish dishes in Thailand. Used raw or added at the last moment, and paired almost always with fish, tamarind and tomato.
- infusing — Added to canh chua in the last moment before serving, often with the pot already off the heat. A few minutes of boiling turns it dull and grassy.
Storage and freshness
| Form | Good for | Conditions | Fridge |
|---|---|---|---|
| Fresh | 0–0 months (typically 0 months) | Stems in water, or wrapped and refrigerated for a day or two. | Yes |
Rub a leaf: fresh rice paddy herb gives lemon and cumin at once, and a limp bunch that smells of nothing much has gone.
- Limp, translucent stems
- Blackened leaves
- Slime at the cut ends
- Loss of the volatile terpene fraction
- Wilting and rot of the soft stems
Quality is not the same as safety
A raw herb from wet ground, handled like any leafy green: washed well, kept cool, and discarded once slimy.
Forms
The form the sources describe, and so the one this page is about.
Fresh stems and leaves
Bunches of soft stems. The only form in which it is used.
Citric and cumin-like.
Chopped, stems included, and stirred into sour soups and curries at the very end, or eaten raw from the herb plate.
Botany
Plantaginaceae
Formerly placed in the Scrophulariaceae, and still listed there in older references.
A soft, sprawling herb of shallow water and wet mud, with succulent stems and small toothed leaves arranged in whorls or opposite pairs, and small purple-pink tubular flowers. It grows wild among rice and in ditches.
Commonly confused with
Sold beside it and named with the same Vietnamese word, ngò. Culantro is a long serrated leaf with a heavy coriander smell; rice paddy herb is a small soft leaf that smells of lemon and cumin. They are not interchangeable in canh chua.
Another herb from the same Vietnamese herb plate, and another one sold under a misleading coriander name. Rau răm is peppery and coriander-like; rice paddy herb is citric and cumin-like.
How it is grown
The plant, how it is propagated and farmed, what threatens the crop, and where it is produced now. Crop diseases here are plant health, not food safety.
The leaves and soft stems of a fleshy herb of shallow water, variable enough to behave as an annual or a perennial, growing 30–100 cm tall in ponds and marshy ground from sea level to about 1,000 m.
Where it comes from and how it is made
Tropical Asia, from India through Southeast Asia to southern China and northern Australia, as a native of wetlands.
- Vietnam (Mekong Delta) — notable producer. Where the herb is most used and most grown.
- Thailand — notable producer
- Cambodia — notable producer
Stem tips cut and bunched; the plant regrows.
- Cutting — Soft stem tips cut and sold in bunches, stems and all.
Gathered from rice fields and grown in wet beds or pots of mud; outside Southeast Asia it is mostly grown by Vietnamese growers for diaspora markets, and by aquarium keepers, who know it as an aquarium plant.
Hot and waterlogged. It is a plant of flooded paddies and ditches, grows in standing water, and does not survive frost.
Buying and quality
Fresh or not at all. Buy it the day you cook with it and keep the stems in water; if you grow it, a tub of wet mud on a warm windowsill is enough.
- Asked for as ngò om at a Vietnamese grocer.
- Upright, firm stems rather than limp ones.
- A clear lemon-and-cumin smell when rubbed.
History and trade
A local fresh herb, not a traded commodity; outside Southeast Asia it reaches diaspora grocers in small quantities.
Culture
Recorded by tradition rather than merged into one narrative — these are genuinely different practices.
Southern Vietnam and the Mekong Delta
Ngò om is the finishing herb of canh chua, the sweet-sour soup of fish, tamarind, tomato, pineapple and bean sprouts that is the everyday soup of the delta, usually alongside sawtooth herb and fried garlic. It is thrown in last and is the ingredient southern cooks name when asked why a canh chua made abroad tastes wrong.
- In canh chua
- In sour fish curries
- On the raw herb plate
Northeast Thailand (Isan) and Laos
Isan and Laos (Thailand and Laos).
Eaten raw with fermented-fish dishes and grilled fish, and added to soups and curries of freshwater fish — the same partnership with fish and sourness it has in Vietnam.
- Raw with grilled fish
- In Isan fish soups
What it is called
- Vietnamese: ngò om
- Thai: ผักแขยง (phak khayaeng)
What we do not know
Published openly. A gap we have named is more useful than a gap we have filled with plausible prose.
Not yet established for rice paddy herb:
- Archaeological evidence
- Historical timeline
- Ceremonial use
- Traditional medicinal context
- Regulatory limits
- Traditional uses