Persicaria odorata

Persicaria odorata is a species of flowering plant in the knotweed family, Polygonaceae.<ref name=POWO>Template:Cite web</ref><ref name=COL>Template:Cite web</ref> It is sometimes referred to by the common names Vietnamese coriander, rau răm (from Vietnamese), laksa leaf (calque from Malay daun laksa),<ref name=MBG>Template:Cite web</ref> Vietnamese cilantro, phak phai (from Thai: ผักแพว), praew leaf, hot mint, Cambodian mint<ref name=EPPO>Template:Cite web</ref> and Vietnamese mint,<ref>Template:Cite web</ref> is an herb whose leaves are used in Southeast Asian and Northeast Indian cooking.

But despite its other name, Vietnamese coriander is unrelated to the mints, nor is it in the mint family Lamiaceae, but its general appearance and fragrance are reminiscent of them. It is also not closely related to coriander (family Apiaceae). Persicaria is in the family Polygonaceae, collectively known as "smartweeds" or "pinkweeds". The similarities in the tastes and smells between Persicaria and coriander and mint may be an example of convergent evolution.

Distribution

It is native to Cambodia, China (North-Central, South-Central and Southeast), Hainan, Japan, Korea, Laos, Malaysia, Myanmar, the Ryukyu Islands, Taiwan, Thailand, and Vietnam.<ref name=POWO/>

Food uses

Template:Contains special characters The leaf is primarily associated with Vietnamese cuisine,<ref>Heavenly Fragrance: Cooking with Aromatic Asian Herbs, Fruits, Spices and Seasonings, p.29, Carol Selva Rajah, Tuttle Publishing, 2008</ref> 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).<ref>Template:Cite web Monday, 8 July 2019</ref>

In Malaysia, Singapore and Indonesia the shredded leaf is an essential ingredient of several variations of laksa, a spicy noodle soup, so much so that the leaf is commonly nicknamed "laksa leaf" (daun laksa). The leaves are otherwise known in Malay and Indonesian as daun kesum and used in dishes like nasi kerabu and asam pedas.Template:Cn

In the cuisine of Cambodia, the leaf is known as chi krasang tomhom (Template:Langx) and is used in soups, stews and salads. It is also used in naem (ណែម), Cambodian summer rolls.Template:Cn

In Laos and certain parts of Thailand, the leaf is eaten with raw beef larb (Template:Langx).Template:Cn

In Burmese cuisine, the leaves are called phetphe (Template:Linktext) and used in various Burmese curries.<ref>Template:Cite web</ref> The leaves are locally known as phak phai in neighbouring Manipur, India. The Khoibu community grind the leaves with ghost pepper and a nut locally known as "bonra" to make a spicy side dish.Template:Cn

In Australia, 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.<ref name=HM/>

Characteristics

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 Template:Convert in height and spread up to Template:Convert.<ref>Template:Cite web</ref> 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.

Components

Vietnamese coriander oil contains aldehydes such as decanal (28%), and the alcohols dodecanol (44%) and decanol (11%). Sesquiterpenes such as α-humulene and β-caryophyllene comprise about 15% of its oil.<ref name=HM>Template:Cite journal</ref>

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.<ref>Template:Cite journal</ref>

Traditional uses

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.<ref>Vietnamese Coriander (Persicaria odorata (Lour.) Soják) page from Gernot Katzer's Spice Pages</ref>

Cultivation

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 Template:Convert 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 Template:Convert) with West and South facing aspects preferable.

Persicaria odorata grows up to Template:Convert tall and wide in US and UK sources state Template:Convert 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.

Propagation

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 Template:Convert roots appear below the lowest node and then plant in soil. Expect to harvest around two months later.<ref name=JSS>Template:Cite web</ref><ref name=RHS>Template:Cite web</ref>

External links

• How to grow Persicaria odorata
• Vietnamese instructional video on Persicaria odorata cultivation and propagation
• English language instructional video on Persicaria odorata cultivation and propagation