TAXONOMIC PRINCIPLES 



19 



Miocene 



Oligocene 



Fig. 2-2. Schematic representation of the suggested origin and 

 evolution of present day Hymenopappus species (Turner, 1956). 



various taxa, as determined from degrees of specialization, are in- 

 dicated, the factor of time for the assumed branching is not indicated. 

 The diagram indicates that D. torulosa is morphologically the 

 most speciahzed, or advanced, and that D. chrysantha is the most 

 primitive. In terms of position, as determined from the morphology of 

 the characters selected, D. torulosa is closer to D. scandens than it 



