Vietnamese balm

Vietnamese balm is an annual herb 30–80 cm tall with a slender, short-hairy, much-branched square stem. The leaves are opposite, ovate to ovately pointed with evenly serrate margins, dark green above and paler beneath, and both surfaces carry oil-bearing glandular hairs, so lightly bruising the foliage releases a strong lemony scent. The small pale-purple to pinkish-white flowers crowd into dense spikes at the shoot tips and in the upper leaf axils, the spikes usually one-sided; the corolla is tubular with an upper and a lower lip, as in the mint family. Flowering is staggered from July to September and is followed by four small nutlets. The erect plant gives off a clear lemon-mint aroma as soon as the leaves are touched.

According to Kew's Plants of the World Online the native range of Elsholtzia ciliata is temperate Asia to Peninsular Malaysia, covering Afghanistan, Mongolia, Siberia and the Russian Far East (Altay, Amur, Buryatia, Chita, Irkutsk, Primorye, Khabarovsk, Sakhalin, the Kurils, Kamchatka), China (north-central, south-central, south-east, Inner Mongolia, Tibet), the East and West Himalaya, Nepal, Japan, Korea and Taiwan, plus continental Southeast Asia (Vietnam, Laos, Cambodia, Thailand, Myanmar, Malaya). Flora of China records it from 0–3400 m on hillsides, waste ground, sunny terraces, riverbanks and open forest, in every Chinese province except Qinghai and Xinjiang. It has been introduced into Europe (Germany, Poland, Sweden, Denmark, Ukraine, Romania, European Turkey) and North America (several north-eastern US states as well as Ontario and Québec), where EPPO lists it as an introduced, potentially weedy species. In Vietnam it both grows wild on moist ground and field margins and is sown around houses as a culinary herb.

Steam distillation of the whole plant yields about 0.82% essential oil on a dry-weight basis (Vietnam Journal of Science and Technology, 2023). Composition depends strongly on provenance: in Vietnamese-grown material the oil is dominated by the citral pair — geranial 19.5–26.5% and neral 15.2–20.5% — with limonene 10.9–14.2% and (Z)-β-farnesene 10.8–11.7%, plus linalool, nerol, geraniol and the formiate and acetate esters of nerol and geraniol (Dũng, Lê Văn Hác, Lê Huy Hải and Leclercq, Journal of Essential Oil Research, 1996). A Vietnamese sample analysed in 2023 gave (Z)-β-farnesene 22.72%, neral 15.66%, geranial 15.62% and β-ocimene 13.30%. By contrast, oil from temperate regions is dominated by the two furan-containing ketones characteristic of the genus Elsholtzia: dehydroelsholtzia ketone at 66.1–72.4% in material from Novosibirsk (Russia, 2002), while a sample collected in Vilnius (Lithuania, 2022) contained 86.23% dehydroelsholtzia ketone and 10.64% elsholtzia ketone (elsholtzione). The signature lemon scent of Vietnamese kinh giời therefore comes from citral, whereas the genus-level chemical marker is that pair of furanoid ketones.

Culinary use is central: Vietnamese balm is the raw herb served with bún bò Huế beef noodles, rice porridge, salads and balut, while Vietnamese folk medicine decocts the whole plant for colds, headache and a fever that does not break with sweat. Research shows the essential oil inhibits both gram-negative and gram-positive bacteria (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Proteus mirabilis), scavenges radicals in the DPPH assay (IC50 26.55 g/L) and is toxic to HepG2 liver cells in vitro (IC50 0.00204%), as published in the Vietnam Journal of Science and Technology in 2023; Ma et al. (Journal of Essential Oil Bearing Plants, 2018) likewise reported antibacterial and antioxidant activity in supercritical-fluid extracts. Most importantly, a pharmacological study published in Pharmaceuticals in 2023 found that the oil reduced phenylephrine-induced contraction of rat prostate strips and aortic rings in a concentration-dependent manner (IC50 0.24 and 0.72 µL/mL respectively) through antagonism of α1-adrenergic receptors — a potential basis for smooth-muscle relaxation and blood-pressure lowering, consistent with an earlier hypotensive report in pigs.

On safety, Vietnamese balm is generally safe at normal culinary doses, but concentrated essential oil should not be taken undiluted or applied neat because it irritates mucosa and skin. Pregnant women and people taking antihypertensive or erectile-dysfunction medication should consult a practitioner before high or prolonged use, since the oil antagonises α1-receptors and can lower blood pressure; no studies exist for infants, so the oil should not be applied to a baby's skin. For conservation, the data held in this dictionary place the species in the Least Concern (LC) category and it is not listed in CITES; it is very widely distributed, seed-prolific and adaptable, so it is not threatened. In parts of its introduced range in Europe and North America it can behave as a weed competing with native plants. Conservation priorities are to protect native wild populations in Vietnam and to conserve chemical diversity between chemotypes — the citral type in the tropics and the furan-ketone type in temperate regions — by sowing locally collected seed, avoiding hybridisation with other Elsholtzia species and refraining from over-harvesting where populations are small.