Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class cations [X+]
                 Class onium compounds
                   Class oxonium ions [R3O+]
                     1 oxonium [H3O+]
                     2 Class hydrocarbylidyne oxonium ions [RC≡O+]