Phylogenetic tree of Type I and Type II KS domains from prokaryotic and eukaryotic PKS and fatty acid synthase (FAS). Type I and Type II KS domains from 60 taxa analysed by maximum likelihood approach. Type II PKS and acyl carrier protein synthases (ACPS) were assigned as outgroups. Approximate likelihood fraction (aLRT) and bootstrap values (BT) ≥ 50% are displayed on appropriate branches as aLRT/BT. (A) The dinoflagellate KS sequences form a well-supported group within the protistan Type I FAS/PKS clade, consistent with previous topology estimates; (B) The dinoflagellate KS group splits into two distinct clades; one contains sequences from different species, the other clade consists exclusively of K. brevis sequences.