Abstract: Three populations of Spartina alterniflora were introduced from Moreherd City, North Carolina; Sapelo Island, Georgia; and Tampa Bay,Florida to China. To find out whether they are ecotypes or ecophenes, the following methods were employed: determination of membrane permeability, contents of amino acids and ions of potassium and sodium, photosynthetic rate and dark respiration in saline environments. Great differences were obtained among the three populations, thus providing evidence of differentiation into the three ecotypes. This is the result of ecotype differentiation for long-time selection of different environments and adaptation of the Spartina alterniflora genetype. In regard to salinity resistance, the Floridaecotype is the most sensitive; the georgiaecotype is the most tolerant; the North Carolinaecotype is intermediate.