Polygonum odoratum Lour. 1790
Persicaria odorata, with common names Vietnamese coriander, rau răm, laksa leaf, Vietnamese cilantro, phak phai, praew leaf, hot mint, Cambodian mint and Vietnamese mint, is a herb whose leaves are used in Southeast Asian and Northeast Indian cooking.
Vietnamese coriander is not related to the mints, nor is it in the mint family Lamiaceae, but its general appearance and fragrance are reminiscent of them. Persicaria is in the family Polygonaceae, collectively known as "smartweeds" or "pinkweeds".
Primarily the leaf is identified with Vietnamese cuisine, where it is commonly eaten fresh in salads (including chicken salad) and in raw gỏi cuốn, as well as in some soups such as canh chua and bún thang, and stews, such as fish kho tộ. It is also popularly eaten with trứng vịt lộn (fertilized duck egg).
However, in Malaysia, Singapore and Indonesia, the shredded leaf is an essential ingredient of the popular laksa dish, a spicy noodle soup, so much so that the leaf is commonly referred to as "laksa leaf" (daun laksa). The Malays called the leaves 'daun kesum' and is used in Malaysia for the dishes nasi kerabu and asam pedas.
The Vietnamese coriander is a perennial plant that grows best in tropical and subtropical zones in warm and damp conditions. In advantageous conditions, it can grow up to 15–30 cm (6–12 in). The top of its leaf is dark green, with chestnut-colored spots, while the leaf's bottom is burgundy red. The stem is jointed at each leaf. In Vietnam, it can be cultivated or found in the wild. It can grow very well outside in summer in nontropical Europe. It prefers full sun and well-drained soil. For colder climate zones, they should be brought inside for the winter and treated as a house plant. For climate zones that have milder winters, they will survive outside, although their growth may slow down. It rarely flowers outside the tropics.
C-Methylated homoisoflavanones (3-(4'-methoxy-benzyl)-5,7-dihydroxy-6-methyl-8-methoxy-chroman-4-one, 3-(4'-methoxy-benzyl)-5,7-dihydroxy-6,8-dimethyl-chroman-4-one, 3-(4'-hydroxy-benzyl)-5,7-dihydroxy-6,8-dimethyl-chroman-4-one, 3-(4'-hydroxy-benzyl)-5,7-dihydroxy-6-methyl-8-methoxy-chroman-4-one and 3-(4'-hydroxy-benzyl)-5,7-dihydroxy-6-methyl-chroman-4-one) can be found in the rhizomes of P. odoratum.
No scientific studies have measured P. odorata's effects on libido. Traditionally, in Vietnam, the herb is believed to repress sexual urges. A saying in Vietnamese states, "rau răm, giá sống" ("Vietnamese coriander, raw bean sprouts"), which refers to the common belief that Vietnamese coriander reduces sexual desire, while bean sprouts have the opposite effect. Many Buddhist monks grow coriander in their private gardens and eat it frequently, believing it helps them remain celibate.
North American sources state Persicaria odorata can be grown outside in frost free parts of USDA Zones 9-11 in moderately fertile soil which is poor or well-drained but will remain moist to wet. It can tolerate full sun if there are breezes and boggy moist soil. However, part shade is desirable and it can be used as groundcover under trees. If winter temperatures drop below 7°C/45°F overwintering indoors is possible if humidity can be maintained. Northern European sources proscribe all but summer under glass as it is hardy to H1C (minimum 5-10°C) with West and South facing aspects preferable. Persicaria odorata grows up to 6-18 inches tall and wide (15-45 cm) in US and UK sources state 1 metre height by 1.5 m spread are possible in 2 to 5 years. Pests and diseases are not regarded as being problematic and it is even resistant to deer and rabbit.
Propagate by seed in autumn or spring but flowering and seed harvests are rare in non tropical climes. In summer, propagation via semi-ripe cuttings should be straightforward. Rooting cuttings in water is so easy that North American sources recommend against overwintering indoors where humidity cannot be maintained. Rather, source fresh bunches of rau răm in early spring cost effectively from Asian supermarkets. Remove the young leaves at the very top of the stems and any large leaves along the stems. Trim the bottom off stems to the first healthy internode and place in water until 1-2 cm roots appear below the lowest node and then plant in soil. Expect to harvest around two months later.
- Tropicos, Persicaria odorata (Lour.) Soják
- "Persicaria odorata at MBG". Missouri Botanical Garden. Retrieved 12 April 2022.
- "Persicaria odorata". European and Mediterranean Plant Protection Organization (EPPO). Retrieved 15 May 2021.
- "Persicaria odorata". New South Wales Flora Online. Retrieved 9 January 2023.
- Heavenly Fragrance: Cooking with Aromatic Asian Herbs, Fruits, Spices and Seasonings, p.29, Carol Selva Rajah, Tuttle Publishing, 2008
- "Vietnamese Coriander". Monday, 8 July 2019
- Kesom Oil – a New Essential Oil for the International Flavour and Fragrance Industry in First Australian New Crops Conference 1996 – Volume 2 Archived 2006-09-19 at the Wayback Machine
- A new C-methylated homoisoflavanone and triterpenoid from the rhizomes of Polygonatum odoratum. Wang D, Li D, Zhu W and Peng P, Natural Product Research, 2009, 23:6, pages 580-589, PMID 19384735
- Vietnamese Coriander (Persicaria odorata (Lour.) Soják) page from Gernot Katzer's Spice Pages
- "Persicaria odorata at gardenia.net". Jardins Sans Secret LLC, 210 E 61st St, NY 10065. Retrieved 12 April 2022.
- "Persicaria odorata at RHS". The Royal Horticultural Society. Retrieved 12 April 2022.