Flax (Linum usitassimum L.) of family Linaceae is one of the most important crops, which has been widely used from ancient times. The aim of the study was to examine seed morphological characteristics and fatty acids differences among 13 populations of flax (11 from Iran, one from Turkey and one from USA). We studied six morphological variables of seeds in 50 replications. The methyl esters of seeds fatty acids were analyzed using GC. We detected that the flax seeds shape and color were stable among the populations, whereas ANOVA proved significant variations for all the quantitative seed morphological features. Moreover, we found the main fatty acids of the seed oil remained consistent over the ecological and geographical ranges of the populations, except for Khorasan and Turkey populations differed from the rest by their second main fatty acid. We registered that the amounts of main fatty acids differed among the populations and ANOVA test proved significant differences for most of the identified fatty acids. In addition, significant relationships were registered between some fatty acids. The populations were clustered in UPGMA tree and PCO plot into three distinct groups. CA joined plot and PCA biplot demonstrated that each group had specific type and amount of fatty acid. Therefore, we defined three chemotypes: petroselinic acid, linoleic and linolenic acids, and oleic acid. Although, studied ecological factors influenced ome fatty acids amounts, populations from different phytogeographical regions clustered closely as chemotypes. This revealed that populations of each chemotype have been originated from the same diversity center, and some secondary diversity centers exist for flax in the world.
