Note: Many botanists divide the Ph[ae]nogamia primarily into
      Gymnosperms and Angiosperms, and the latter into
      Dicotyledons and Monocotyledons. Others consider
      Pteridophyta and Bryophyta to be separate classes.
      Thallogens are variously divided by different writers,
      and the places for diatoms, slime molds, and stoneworts
      are altogether uncertain. For definitions, see these
      names in the Vocabulary.