Persicaria odorata

Persicaria odorata, with common namesVietnamese coriander,rau răm,laksaleaf(calque from Malay 'daun laksa'),Vietnamese cilantro,phak phai(fromThai: ผักแพว),praew leaf,hot mint,Cambodian mintandVietnamese mint,is an herb whose leaves are used in Southeast Asian and Northeast Indian cooking.
But despite its other name, Vietnamese coriander is unrelated to themints, nor is it in the mint familyLamiaceae, but its general appearance and fragrance are reminiscent of them. It is also not closely related tocoriander(familyApiaceae).Persicariais in the familyPolygonaceae, collectively known as "smartweeds" or "pinkweeds". The similarities in the tastes and smells betweenPersicariaand coriander and mint may be an example ofconvergent evolution.
The leaf is primarily associated withVietnamese cuisine,where it is commonly eaten fresh in salads (includingchicken salad) and in rawgỏi cuốn, as well as in some soups such ascanh chuaandbún thang, and stews, such as fishkho tộ. It is also popularly eaten withtrứng vịt lộn(fertilizedduckegg).
InMalaysia,SingaporeandIndonesiathe shredded leaf is an essential ingredient of several variations oflaksa, a spicy noodle soup, so much so that the leaf is commonly referred to as "laksa leaf" (daun laksa). The leaves are otherwise known in Malay asdaun kesumand used in dishes likenasi kerabuandasam pedas.
In theCambodian cuisine, the leaf is known aschi krasang tomhom(Khmer:ជីរក្រសាំងទំហំ) and is used in soups, stews and salads. It is also used innaem(ណែម), Cambodian summer rolls.
InLaosand certain parts ofThailand, the leaf is eaten with raw beeflarb(Lao:ລາບ).
InBurmese cuisine, the leaves are calledphetphe(ဖက်ဖယ်) and used in variousBurmese curries.The leaves are locally known asphak phaiin neighbouringManipur,India. TheKhoibucommunity grind the leaves withghost pepperand a nut locally known as "bonra" to make a spicy side dish.
InAustralia, Persicaria odorata is being investigated as a source of essential oil (kesom oil). Research conducted in North East Victoria has shown that kesom oil has potential applications in the flavor and fragrance industry, particularly as a natural source of aliphatic aldehydes.
The Vietnamese coriander is aperennial plantthat 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 inches) in height and spread up to 60 cm (24 inches).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.
Its oil containsaldehydessuch asdecanal(28%), and the alcoholsdodecanol(44%) anddecanol(11%).Sesquiterpenessuch asα-humuleneandβ-caryophyllenecomprise about 15% of its oil.
C-Methylatedhomoisoflavanones(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-oneand3-(4'-hydroxy-benzyl)-5,7-dihydroxy-6-methyl-chroman-4-one) can be found in the rhizomes ofP. odoratum.
No scientific studies have measuredP. 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.  ManyBuddhistmonks 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 ofUSDA Zones9-11 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 ishardyto H1C (minimum 5–10 °C (41–50 °F)) with West and South facing aspects preferable.
Persicaria odorata grows up to 6 to 18 inches (150 to 460 mm) tall and wide in US and UK sources state 1 by 1.5 metres (3 ft 3 in × 4 ft 11 in) 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 healthyinternodeand place in water until 1–2 centimetres (0.39–0.79 in) roots appear below the lowest node and then plant in soil. Expect to harvest around two months later.