The term megadiverse country refers to any one of a group of nations that harbor the majority of Earth's species and high numbers of endemic species. Conservation International identified 18 megadiverse countries in 1998. Many of them are located in, or partially in, tropical or subtropical regions. Mega diversity means exhibiting great diversity. The main criteria for megadiverse countries is endemism at the level of species, genera and families. A megadiverse country must have at least 5,000 species of endemic plants and must border marine ecosystems.