Kingdom Chlorobiota C.Jeffrey ex Doweld (2001) - plants see Subkingdom Viridiplantae Caval.-Sm. (1981)
   Subkingdom Pteridobiotina Britton & A. Br. (1896)
     Superdivision Cycadophytanae Doweld (2001) see Superphylum Cycadophytanae Doweld (2001)
       Division Cycadophyta Bessey (1907)
         Class †Cycadeoideopsida D.H.Scott (1923) [monotypic]
           Order †Cycadeoideales E.W.Berry (1916)
             Family †Williamsoniellaceae Nakai (1943)
               1 Genus †Wielandella orth. inval. see Genus Wielandiella Nath. (1910)
               2 Genus †Williamsoniella H.H.Thomas (1915)