Nerodia clarkii is a collective term assigned to a group that includes three subspecies (Conant and Collins 1998) of salt marsh snakes, 2 of which are found in the Indian River Lagoon system: the Atlantic Salt Marsh Snake, Nerodia clarkii taeniata; and N. clarkii compressicauda, the mangrove salt marsh snake. The Federally listed Atlantic Salt Marsh Snake, N. c. taeniata can breed with other subspecies of salt marsh snakes and also with a freshwater subspecies, Nerodia fasciata, producing hybrids with various mixtures of physical characteristics. Its original origin is unknown. The taxonomy of the salt marsh snakes has been, and continues to be somewhat controversial. Some experts have postulated N. c. taeniata is a relict hybrid produced from other snake subspecies during the Pleistocene (1.8 million years ago to 11,000 years ago). Others suggest that it is not truly a unique subspecies, but a population of N. c. compressicauda that has developed different physical characteristics in response to different selective pressures (Kochman 1992).Nerodia c. compressicauda, the Mangrove Salt Marsh Snake, is the larger of the 2 subspecies and has little to no dorsal striping. It also has a unique red phase that helps it blend in with the prop roots of mangroves. The threatened Atlantic Salt Marsh Snake, Nerodia c. taeniata, is the smallest of the salt marsh snakes and has a maximum length of 61 cm (2 feet) (Conant and Collins 1998). Its dorsal body coloration is generally rust to brown or olive, with 2 longitudinal stripes along each side of the body. The stripes eventually fragment near the tail and appear as blotches. The ventral surface has 1 row of pale colored spots. There are 21 - 25 scale rows at midbody, and the scales are keeled. The anal plate is divided.