Betel

Betel is an evergreen climbing vine with smooth stems 3–10 m long that cling by adventitious roots at the nodes; the plant is dioecious. The alternate leaves have a heart-shaped, slightly unequal base, blades 8–12 cm long, a glossy waxy upper surface and often a pinkish midrib and petiole; the leaf is crisp and releases a pungent aromatic smell when crushed. Flowers are tiny, unisexual and pale yellow in long catkins; the round berries ripen red but are rarely seen because the plant is grown mainly from cuttings.

According to Kew's Plants of the World Online, betel is native from Indochina to Malesia — Vietnam, Cambodia, Laos, Myanmar, Thailand, Peninsular Malaysia, the Philippines, the Lesser Sunda Islands and the Andaman–Nicobar Islands. Along trade and migration routes it spread to India, Sri Lanka, Bangladesh, the Pacific (New Guinea, Fiji, Vanuatu) and on to Madagascar, East Africa and the Caribbean. The vine needs a pole or trellis to climb and well-drained fertile soil, avoiding waterlogged or saline ground; in the humid tropics it is typically grown on small home trellises.

The leaf is the medicinal part and yields about 4.2% essential oil. Its hallmark constituents are allylphenols: chavibetol (with chavibetol acetate giving a clove-like pungency), hydroxychavicol (allylpyrocatechol/2-hydroxychavicol, up to ~26% in some cultivars), together with eugenol, chavicol, methyl eugenol and safrole; there are also sesquiterpenes (β-caryophyllene), monoterpenes (1,8-cineole, α-pinene, camphene), flavonoids (quercetin, luteolin, apigenin), tannins and β-sitosterol. The content and ratio of these compounds vary widely with cultivar, season and locality — chavibetol/hydroxychavicol typify Vietnamese and Indian types, whereas safrole dominates some Sri Lankan cultivars.

Studies support many activities of hydroxychavicol and eugenol: antifungal action against 124 strains (MIC 7.81–62.5 µg/mL for dermatophytes; Ali et al., Ann Clin Microbiol Antimicrob, 2010), xanthine-oxidase inhibition (Murata et al., J Nat Med, 2009), antimutagenic activity (Amonkar et al., Food Chem Toxicol, 1986) and preclinical anti-inflammatory and anticancer effects (AACR Cancer Prev Res, 2014; J Cell Mol Med, 2022). Culturally the leaf is central to betel chewing — offered to guests, used in worship and weddings; chewing stimulates salivation, gives mild refreshment and freshens the mouth. Young leaves are also eaten raw or used to wrap food, and extracts are studied for mouthwash, antimicrobials, food preservatives and natural antioxidants.

A key distinction must be made between the leaf and the chew: IARC Monographs Vol. 85 (2004) classifies betel quid chewed with areca nut (and areca nut itself) as Group 1, carcinogenic to humans, linked to oral and oesophageal cancer; the leaf alone is not in this group, but the betel-quid habit is addictive and harms oral health, so it should be limited. The oil and chavicol can irritate skin and mucosa, and high internal doses are unsafe in pregnancy. Piper betle is Not Evaluated by the IUCN and is not listed by CITES; however, shrinking betel-chewing customs are eroding many valuable local cultivars, so germplasm conservation matters.