Protoctista Hogg, 1860
   Bacillariophyta Engl. & Gilg (1919) - diatoms see [unranked] Diatomea Kütz. (1844)
     Coscinodiscophyceae Round & R.M. Crawford (1990) - radial centrics
       Coscinodiscophycidae Round & R.M. Crawford (1990)
         Melosirales R.M. Crawford (1990)
           Hyalodiscaceae R.M. Crawford (1990)
             Podosira Ehrenb. (1840)