Acmella oleracea, also known under its old names Spilanthes oleracea and Spilanthes acmella, is a flowering herb in the plant family Asteraceae, also known as toothache plant or paracress as the leaves and flower heads contain an analgesic agent spilanthol used to numb toothache. It is native to the tropics of Brazil, and is grown as an ornamental (and occasionally as a medicinal) in various parts of the world. A small, erect plant, it grows quickly and sends up gold and red flower inflorescences. It is frost-sensitive but perennial in warmer climates. Vernacular names The English common name, toothache plant, is synonymous with the Swedish common name tandvärksplanta; both stem from the analgesic alkylamides the plant contains. The name paracress is in reference to the Northern Brazil state Pará. It is known in French as brède mafane and cresson de Para, and in Portuguese as agrião do Pará and jambú.  Culinary uses For culinary purposes, small amounts of shredded fresh leaves add a unique flavour to salads. Cooked leaves lose their strong flavour and may be used as leafy greens. Both fresh and cooked leaves are used in dishes in parts of Brazil, often combined with chillies and garlic to add flavor and vitamins to other foods. A related species is used in several Southeast Asian dishes. Consumption of portions or whole flowers have been reportedly used to offset the intense heat of chillies and peppers.  Popular uses A decoction or infusion of the leaves and flowers is recommended for stammering, toothache, stomatitis and throat complaints. Eating a whole flower bud results in an extremely strong tingling sensation accompanied by excessive saliva production.  Properties The most important taste-active molecules present are the alkamides and especially, (2E,6Z,8E)-deca-2,6,8-trienoic acid N-isobutyl amide or spilanthol,
which is responsible for the trigeminal and saliva-inducing effects of products such as Jambu oleoresin, a concentrated extract from Paracress. Extracts using hexane of freshly harvested flowers of S. acmella were bioassayed against A. aegyptii larvae and H. zea (corn earworm) neonates. Mosquitocidal assays on A. aegyptii using spilanthol indicated that they were very active. Spilanthol had a LD100 (24 h) at 12.5 µg/mL concentrations and showed 50% mortality at 6.25 µg/mL. The mixture of isomers of spilanthol showed a 66% weight reduction of H. zea neonate larvae at 250 µg/mL concentration after 6 days. Acmella oleracea has also been shown to have a strong diuretic action in rats. Acmella oleracea extract has been tested against various yeasts and bacteria and was essentially inactive. Besides the main active ingredient spilanthol, Acmella also contains stigmasteryl-3-O-b-D-glucopyranoside and a mixture of triterpenes. The isolation and total synthesis of the active ingredients have been reported.