Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class onium compounds
                 1.1.2 Class ammonium compounds [R4N+X-]
                 1.1.3 Class iminium compounds [R2C=NR2]+X-
                 1.2.2 Class phosphonium compounds [[R4P]+X-]
                 1.3.2 Class arsonium compounds [[R4As]+X-]
                 1.4.2 Class stibonium compounds [[R4Sb]+X-]
                 2.2.2 Class sulfonium compounds [[R3S]+X-]