Abstract A phylogenetic hypothesis is presented illustrating relationships among 23 extant sturgeon species based on nucleotide data from five mitochondrial genes (cytochrome b, NADH5, control region, 16S, and 12S). The tree supports our previous hypotheses regarding relationships among species of Acipenser and Huso. The introduction of Scaphirhynchus and Pseudoscaphirhynchus to the analysis does not change these main relationships. The genera Scaphirhynchus and Pseudoscaphirhynchus do not form a monophyletic group corresponding to the subfamily Scaphirhynchinae or the tribe Scaphirhynchini. The genus Scaphirhynchus may be basal within the family Acipenseridae, whereas Pseudoscaphirhynchus appears to be embedded within Acipenser clustering with the stellate sturgeon, Acipenser stellatus. The morphological similarity between Scaphirhynchus and Pseudoscaphirhynchus could be a result of convergent evolution of different ancestral sturgeon forms in similar environmental conditions of distant river systems of ...