A comparative analysis of the physiology, toxin composition, and ribosomal DNA sequences were performed on a suite of clonal cultures of the potentially toxic dinoflagellate Alexandrium tamarense.These were established from resting cysts or vegetative cells isolated from sediment or the water taken from the coasts of Greenland, Iceland, Chukchi Sea and Gulf of Maine.Results revealed that strains were indistinguishable, both toxin profiles and through the sequencings of the D l-D2 domain of the large subunit.A.tamarense species have been shown to be more toxic at low temperature.No dcGTX2 was detected in all 12 isolates, toxin content significant variation was observed, range from 37.3 to 351.1 fmol/cell.This may indicate that the genetically determined toxin profiles in A.tamarense species are more complex than previously appreciated.All the isolates included in this study merged into the "North America" clade (Group 1).These findings showed that the resolving power of these sequences is not adequate to explain the morphological or physiological differences that exist among these strains.