This study compared the alkaloid contents of Ilex vomitoria and I. cassine L. and assessed alkaloid variation in the former species. Alkaloid contents of I. vomitoria and I. cassine were analyzed by high-pressure liquid chromatography as were leaf samples of different ages from different crown positions of I. vomitoria. Methylxanthines of 110 I. vomitoria shrubs from the field and 24 plants grown under manipulated light and nitrogen conditions were analyzed by liquid chromatography-mass spectrometry.
Methylxanthines are more abundant in I. vomitoria than in I. cassine, and young leaves of the former species are more alkaloid-rich than mature leaves. Ilex vomitoria methylxanthines vary spatially with size and abiotic environmental covariates, but caffeine and theobromine levels respond differently to experimental light and nitrogen conditions. Ilex vomitoria is the best supported candidate source of cassina, and its variable alkaloid content can be partly predicted from spatial and abiotic variables
