Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class alkaloids
                 Class xanthines
                   caffeine [C8H10N4O2]
                   theobromine [C7H8N4O2]
                   theophylline [C7H8N4O2]