Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class cations [X+]
                 Class onium compounds
                   1.1.1 ammonium [H4N+]
                   1.1.2 Class nitrilium ions [RC≡NH+]
                   1.2 phosphonium [H4P+]
                   1.3 arsonium [H4As+]
                   1.4 stibonium [H4Sb+]
                   1.5 bismuthonium [H4Bi+]
                   2.1 Class oxonium ions [R3O+]
                   2.2 sulfonium [H3S+]
                   2.3 selenonium [H3Se+]
                   2.4 telluronium [H3Te+]
                   3 Class halonium ions [R2X+ (X=halogen)]