In naming the first Gardenia species (Gardenia augusta), John Ellis (the botanist who described Gardenia for the first time) wanted to honor Richard Warner who had helped propagate specimens of the plant in Essex, England.
Warner refused to have the plant named after him as he insisted the plant was actually a jasmine species and not a new genus. The genus Gardenia was subsequently named after Alexander Garden of Charleston, South Carolina who was an American physician and botanist who corresponded with Carlos Linnaeus and John Ellis.
(Staples, G. W. and D. R. Herbst. 2005. A Tropical Garden Flora: Plants cultivated in the Hawaiian Islands and other tropical places. Bishop Museum Press, Honolulu, Hawai’i.)
(Smith, A.C. 1974. Studies of Pacific Island plants. XXVII. The genus Gardenia (Rubiaceae) in the Fijian region. American Journal of Botany 61(2):109-128.)
(Wagner, W. L., Herbst, D. R., and S. H. Sohmer. 1999. Manual of the Flowering Plants of Hawai‘i. Revised Edition. Volume 2. Bishop Museum Special Publication 97. University of Hawai‘i Press, Bishop Museum Press, Honolulu, Hawai’i.)