Upon exposure to chilling temperatures, the mangrove populations of Avicennia germinans (L.) L., Languncularia racemosa (L.) Gaertn., and Rhizophora mangle L. showed various amounts of leaf and plant damage that correlated with their latitudinal origin. Populations of more tropical origin showed the most chilling injury and those of more temperate origin showed less injury. The range of variation in dysfunction and chilling injury was widest among Avicennia populations, intermediate among Laguncularia populations, and narrowest among Rhizophora populations, but in each of the three mangroves, populations from northeastern Mexico had greater chilling tolerance than did those from southern Mexico, Belize, or Panama. Populations from Florida had greater chilling tolerance than did those of Jamaica and St. Croix. The most tolerant to chilling treatments were the Avicennia populations of Texas. In both leaves and roots of more tropical Avicennia plants, the lipid extracts had a greater proportion of oleic acid (18:1) and a lesser amount of linoleic (18:2) than in comparable extracts of plants of more temperate origin, but plants of diverse origin showed no consistent changes in the saturation of fatty acids in lipid extracts after chilling. The ratio of 18:2 to 18:1 for Texas plants was significantly greater than for Belize plants that were grown at temperatures above chilling as well as after chilling, suggesting differences in membrane fluidity based on inherent differences in fatty acid composition. Seeds and recently germinated seedlings as well as plants that had been under laboratory conditions for up to 5.5 years continued to show differences in chilling injury; this also suggested that the differentiation is based on inherited properties.