a. Of or pertaining to a very large natural order of plants (Rubiaceae) named after the madder (Rubia tinctoria), and including about three hundred and seventy genera and over four thousand species. Among them are the coffee tree, the trees yielding peruvian bark and quinine, the madder, the quaker ladies, and the trees bearing the edible fruits called genipap and Sierre Leone peach, besides many plants noted for the beauty or the fragrance of their blossoms.