Citrus (genus Citrus) are a large group of tropical and warm-temperate flowering plants that are of tremendous culinary and commercial importance to humans. Citrus include some of the most popular fruits in the world, including oranges, lemons, limes, grapefruits, and tangerines. They are thought to have been cultivated since at least 3,000 BCE - that's 5,000 years ago! In addition to being grown for their fruits, these plants are also grown as ornamentals or as nectar-providers for bees.