Diatoms are mostly photosynthetic eukaryotes within the heterokont lineage.Variable plastid genome sizes and extensive genome rearrangements have been observed across the diatom phylogeny, but little is known about plastid genome evolution within orderor family-level clades.The Thalassiosirales Glezer & Makarova is one of the more comprehensively studied orders in terms of both genetics and morphology.