Related entry: Oleum Monardae.—Oil of Horsemint

The leaves and flowering tops of Monarda punctata, Linné.
Nat. Ord.—Labiatae.
COMMON NAME: Horsemint.
ILLUSTRATION: Bentley and Trimen, Med. Plants, 208.

Botanical Source.—Horsemint is an indigenous perennial or biennial herb, with a fibrous root. The stems are obtusely angled, hoary pubescent, branched, and 2 or 3 feet high. The leaves are oblong-lanceolate to oblong, remotely and obscurely serrate, narrowed at base, punctate, and petioled. The flowers are yellow, with brown or purple spots, in numerous, dense, axillary whorls. The bracts are large, yellow, and red, lanceolate, obtuse at the base, sessile, and longer than the whorls. The corolla is nearly smooth, ringent, tubular, upper lips spotted with purple, lower lip reflexed, 3-lobed. Calyx elongated, cylindric, 15-nerved, subequally 5-toothed, and hairy in the throat; the teeth are short and rigid, awnless. Stamens 2, elongated, ascending, inserted in the throat of the corolla; anthers linear, cells divaricate at base, and connate at apex (G.—W.).

History and Chemical Composition.—This plant is found growing in sandy fields and barrens from New England to the Gulf of Mexico, and westward beyond the Mississippi flowering during the summer. The entire plant has a rather fragrant odor, and a pleasant, pungent, slightly bitter taste. It contains an abundance of essential oil (Oleum Monardae, U. S. P., 1870) on which its active virtues depend. The oil may be obtained by distillation of the recent herb with water. The plant yields its virtues to alcohol, or boiling water by infusion.

OLEUM MONARDAE, or Oil of horsemint, is of a yellowish, or more often yellowish-red or brownish-red color, and has a sharp taste and an aromatic, pleasant odor. Alcohol readily dissolves it. Below 5° C. (39° F.), it deposits crystals of a stearopten once called monardin, but which has subsequently been shown to be thymol(C10H13OH). H. J. M. Schroeter (Amer. Jour. Pharm., 1888) believes the oil to contain 50 per cent of a hydrocarbon (C10H16), 25 per cent of thymol, which he pronounced to be dextro-gyrate, while thymol from oil of thyme is optically inactive, and oxygenated bodies of the composition C10H18O. He also found small quantities of formic, acetic, and butyric acids in the form of esters. More recently, Prof. Edward Kremers and W. R. Schumann (Proc. Amer. Pharm. Assoc., 1896, p. 238) distilled the flowering herb of Monarda punctata of their own collection, and obtained an amber-colored oil of 0.9307 specific gravity, at 20° C. (68° F.), which yielded to a 10 per cent caustic soda solution, 56 per cent of thymol. The residue distilled with water, yielded an oil containing the hydrocarbon cymene (C10H14), previously shown by Brennan (1895) to occur also in the oil of Monarda fistulosa. Another lot of the herb collected by the same authors before flowering yielded upon distillation 3.39 per cent of oil, while more recently, Kremers and W. E. Hendricks (Pharm. Archives, 1899, Vol. II, p. 73), obtained only 1 per cent of oil from a flowering specimen of the plant. In the latter case, 60 per cent of phenols were present, mostly thymol. Its isomer, carvacrol, may be occasionally present in small quantity. The non-phenol part of the oil contained 10 per cent of an alcohol; furthermore, cymene, and a small quantity of dextro-rotatory limonene.

Ɣ Action, Medical Uses, and Dosage.—Horsemint is stimulant, carminative, sudorific, diuretic, and anti-emetic. The infusion or essence is used in flatulence, nausea, vomiting, and as a diuretic in suppression of the urine, and other urinary disorders. The warm infusion is a stimulating diaphoretic, and has acquired some celebrity as an emmenagogue; it may be drank freely. The oil is extremely sharp and pungent, and applied to the skin, excites heat and redness, and if too long or too closely applied, will produce a painful blister. It is used like peppermint oil internally, and is employed locally in embrocations to relieve pain. The full strength oil may be used upon neuralgic parts. The M. didyma and M. fistulosa may be used as substitutes for the above.

Related Species.Monarda didyma, Linné; Oswego tea. This species grows in the Alleghany Mountains, from North Carolina northward to Canada. In the northern states it often grows along streams and in other wet situations. The flower is composed of a showy, large crimson corolla, and crimson-stained bracts. The stamens are much exserted. It is often cultivated in gardens.

Monarda fistulosa, Linné; Wild bergamot, also called Horsemint. From New England states west and south, growing in thickets. Flowers are in a terminal head, large, and have a greenish, white, light lilac, or blue corolla. It is a variable species. The uses of these two species are similar to those of horsemint. The chemical composition of the oil of this plant is analogous to that of Monarda punctata, carvacrol taking the place of its isomer, thymol, contained in the latter plant. Less than 2 per cent of thymol is present in the oil of M. fistulosa. The latter also contains a crystalline red coloring matter resembling alizarin (see E. J. Melzner and Edward Kremers, Proc. Amer. Pharm. Assoc., 1896, p. 242, and Pharm. Archives, Vol. II, 1899, p. 76).

King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.