Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class hydrocarbons [CxHy] - compounds consisting of carbon and hydrogen only
                 Class olefins
                   Class alkenes [CnH2n] - unsaturated acyclic hydrocarbons having one double bond
                     ethylene [C2H4; CH2=CH2]