In the entry “Ilex Opaca.—American Holly” in the book King’s American Dispensatory (1898; scanned and put online by Henriette Kress), Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr.M., Ph.D. write:
According to the analysis of Dr. F. P. Venable (Amer. Jour. Pharm., 1885, p. 390), the dried leaves [of Yaupon Holly, Ilex vomitoria] contain 0.32 per cent of caffeine, 7.39 per cent of tannin, and 5.75 per cent of ash. Mr. Henry M. Smith (Amer. Jour. Pharm., 1872, p. 216) found 0.011 per cent of a volatile oil, 3.4 per cent of resin, and 0.122 per cent of caffeine. (For a detailed and exhaustive article on Ilex Cassine see monograph by Edwin M. Hale, M. D., Bulletin No. 14, Division of Botany, U. S. Department of Agriculture.)In “Natural Predators of the Puss Caterpillar” (2 March 2010), Jerry Cates writes:
Their [the leaves of Ilex paraguayensis] chief constituent is caffeine, which exists in quantities varying from 0.2 per cent to 1.8 per cent, the average yield (Peciolt) being 0.64 per cent. Tannin (matetannic acid) is present in amounts of from 10 to 16 per cent (A. Robbins, Amer. Jour. Pharm., 1878, p. 273).
Copyright 1995–2017 Henriette Kress
However, recent studies show that the main ingredients in yaupon holly (reported by F. P. Venable in the Amer. Journ. Pharm. 57 (8): 389-90, as tannic acid, 7.39%, and caffeine, 0.27%) are not purgative in nature. Later analyses, according to some reports, have failed to isolate emetics. More to the point, the leaves are presently used as a tea by many Texans, myself included, thankfully without producing the slightest signs of emesis.
Many–though not all–of the plants in the genus Ilex contain caffeine in their leaves and stems. Yerba mate (Ilex paraguayensis) has a considerable history of being used by natives of south America to produce a stimulating tea, and is now imported to the U.S. for use as a coffee and tea substitute. Guayusa (Ilex guayusa) is similarly used as a stimulant by natives in the Equadorian Amazon; assays have found that its leaves contain a higher percentage of caffeine (as much as 2.0%) than any other plant. It, too, has recently been introduced to the U.S. as a stimulating tea.
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