Vietnamese coriander

• rau răm

  Vietnamese

  Rau is simply "herb" or "leafy vegetable", so the name only works whole; rau thơm, the general word for fragrant herbs, means something else.

• daun kesum

  Malay — Malaysia and Singapore

  Also sold as daun laksa, laksa leaf, after the dish rather than the plant — a label that says what it is for, not what it is.

• phak phaiผักไผ่

  Thai

• Vietnamese mint

  English

  A shop name and a wrong one. It is not a mint and does not taste of mint; it is a knotweed relative that tastes of sharp coriander.

Hot-peppery and coriander-like, with a faint tongue-prickling bite and a slightly astringent finish. Eaten raw, it cuts through fat and richness — the reason it is served with duck, eggs and coconut broths.

Coriander-like and sharper: green, soapy-citrus, with a waxy, almost metallic high note. Where coriander is soft, rau răm is pointed.

Mid green, often with a dark maroon chevron across each leaf and reddish stems.

Thin, fairly tender leaves on tough wiry stems; the leaves are picked off and the stems discarded.

• Dodecanal and decanal — Long-chain aliphatic aldehydes that dominate the essential oil and give the waxy, soapy-citrus smell. The same family of compounds carries coriander leaf, which is why the two are mistaken for each other.
• β-Caryophyllene — A woody, faintly peppery sesquiterpene present in substantial amounts, and part of what separates the herb from coriander.(what β-caryophyllene is)

Strip the leaves from the stems, then shred them fine for laksa or leave them whole for a herb plate. Add at the end, off the heat, or at the table. If substituting, coriander leaf with a few mint leaves gives the shape of it without the bite.

A raw herb for rich and sour dishes: shredded over Penang asam laksa and laksa lemak, eaten with the fertilised duck egg and with poultry in Vietnam, folded into chicken salads, and added to the herb plate that goes with soups and rolls. It is almost never cooked for long.

• infusing — Stirred into laksa or a Vietnamese soup at the end, where the heat of the broth releases the aroma. Simmered for long, it goes flat and grassy.
• grinding — Not ground. It is shredded fine for laksa and salads or eaten as whole leaves; bruising releases the aldehydes and dulls quickly.

Crush a leaf. Fresh rau răm smells sharp and coriander-like immediately; a bunch that smells only grassy has gone.

• Limp or yellowing leaves
• Black patches from cold damage
• Slime where leaves were wet

• Volatilisation of the aldehyde fraction
• Wilting and blackening of the leaf

Polygonaceae

A creeping perennial of wet ground with jointed, rooting stems and narrow pointed leaves, each usually marked with a dark chevron near its centre. It rarely flowers in cultivation and is propagated almost entirely from cuttings.

Mainland Southeast Asia — Vietnam and its neighbours — where it grows wild and semi-wild along ditches and paddy margins.

• Vietnam — origin. Grown in household plots and market gardens everywhere, and eaten daily.
• Malaysia — notable producer. As daun kesum, grown for laksa.
• Thailand — notable producer
• Cambodia — notable producer
• Laos — notable producer

Stem tips cut repeatedly through the growing season, the plant regrowing from the nodes below the cut.

1. Cutting — Leafy stem tips cut and bunched for market.
2. Picking over — Leaves stripped from the wiry stems at the table or in the kitchen, since the stems are tough.

A household and market-garden crop rather than a commodity. Stems root wherever a node touches wet soil, so it is grown from cuttings and spreads readily; outside the tropics it is kept as a pot plant brought indoors in winter.

Warm and wet. It grows in saturated soil and shallow water, tolerates shade, and dies back in frost — which is why it thrives where coriander bolts and fails where coriander is easy.

Fresh, always, and a pot rather than a bunch if you use it often: the stems root in a glass of water and the plant grows fast in warmth. Dried rau răm is barely worth buying, because the dishes it belongs in eat it raw.

• Bought from a Vietnamese or Malaysian grocer, often as rau răm or daun kesum rather than under an English name.
• Firm, unwilted leaves with the dark chevron marking visible.
• A sharp smell when a leaf is crushed.
• A rooted pot, where available, which will keep producing on a warm windowsill.

Not traded as a commodity. It reaches Europe, North America and Australia through diaspora grocers, often as potted plants.