The cultivated tomato, Lycopersicon esculentum Mill., a fruit that is almost universally treated as a vegetable, belongs to the nightshade family Solanaceae, which is in Division Magnoliophyta, Class Magnoliopsida, Subclass Asteridae, Order Solanales, and Suborder Solanineae. The family Solanaceae consists of 96 genera and about 2800 species in the three subfamilies Solanoideae, Cestroideae, and Solanineae (Nee et al., 1991). The genus Lycopersicon, which is in the subfamily Solanoideae, is one of the smallest genera in the Solanaceae and the closest to the genus Solanum (nightshade). Originally, Linnaeus included the tomato in Solanum; however, in 1754 Miller separated tomatoes and designated the genus Lycopersicon (Warnock, 1988). Some researchers today wish to treat Lycopersicon under the genetic heading of Solanum (Spooner et al., 1993). There are nine known species in the genus Lycopersicon, including the cultivated tomato and its wild form, L. esculentum var. cerasiforme (Dun.) Gray, and eight wild species: L. pimpinellifolium (Jusl.) Mill.; L. cheesmanii Riley; L. chmielewskii Rick, Kes., Fob., & Holle; L. chilense Dun.; L. parviflorum Rick, Kes., Fob., & Holle; L. peruvianum (L.) Mill.; L. hirsutum Humb. & Bonpl.; and L. pennellii (Corr.) D’Arcy (Rick, 1976a, 1979b). All species are native to western South America, between Ecuador and Chile, although L. esculentum var. cerasiforme (wild cherry) is also found in Mexico, Central America, and other parts of South America. The natural habitat of the Lycopersicon is highly variable, from very dry to very wet and from coastal areas to mountainous elevations of more than 3300 m (Warnock, 1988). This diversity in natural habitat has undoubtedly contributed to the great variation that can be found in Lycopersicon.