The opossum (/əˈpɒsəm/ or /pɒsəm/) is a marsupial of the order Didelphimorphia (/daɪˌdɛlfɪˈmɔːrfiə/) endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 103 or more species in 19 genera. Opossums originated in South America and entered North America in the Great American Interchange following the connection of the two continents. Their unspecialized biology, flexible diet, and reproductive habits make them successful colonizers and survivors in diverse locations and conditions. In the United States and Canada, the only species found is the Virginia opossum, and it is generally referred to as a "possum" - but should not be confused with the suborder Phalangeriformes, which are arboreal marsupials in the Eastern Hemisphere also called "possums" because of their resemblance to Didelphimorphia.