Since the first printing of Carl Linnaeus's Species Plantarum in 1753, plants have been assigned one epithet (name) for their species and one for their genus, a grouping of related species. Thousands of plant genera (genuses) have been named for people, including botanists (and their colleagues and friends), plant collectors, horticulturists, explorers, rulers, politicians, clerics, doctors, philosophers and scientists. Even before Linnaeus, botanists such as Joseph Pitton de Tournefort, Charles Plumier and Pier Antonio Micheli were naming plants for people, sometimes in gratitude for the financial support of their patrons.