Rau răm is the Vietnamese herb also called Vietnamese coriander, known for its peppery flavor in salads and soups.
Rau răm is the Vietnamese name for Persicaria odorata, a tropical herb in the buckwheat family. Its narrow leaves have a flavor that is often described as peppery, citrusy, or coriander-like, although it is not a true member of the coriander family.
The herb is used fresh rather than as a dried spice. It appears with salads, rice-paper rolls, noodle dishes, soups, and boiled duck eggs. In Vietnamese cooking, it can provide a sharp aromatic contrast to rich meats, seafood, and mildly sweet sauces.
English-language sources may call it Vietnamese coriander, Vietnamese mint, or laksa leaf. Those names can cause confusion because rau răm is botanically distinct from both coriander and mint. The scientific name Persicaria odorata is the clearest way to identify the plant.