The Origin of Crepis and Related Genera, with 



Particular Reference to Distribution and 



Chromosome Relationships 



By Ernest Brown Babcock 



THE PHYLETic RELATIONS of the gcnus Crepis cannot be 

 adequately discussed without some consideration of 

 nearly related genera. Although none of these other 

 genera has been as thoroughly studied as Crepis, sufficient in- 

 formation is available to indicate rather definitely that the posi- 

 tion of Crepis with reference to its closest allies is unique. In 

 order to make this clear, it is proposed, first, to review the evi- 

 dence on comparative morphology, chromosome number, and 

 geographic distribution of these closely related genera so as to 

 present, as clearly as possible in brief and rather general form, a 

 review of this small portion of the Compo sitae; and, second, to 

 summarize the much more detailed information now available 

 concerning Crepis, in order to see what further light this may 

 throw on the problem of origin. But, before discussing this 

 group of genera, a few remarks on criteria of relationship may 

 be in order. 



This subject has been discussed by the present writer in an 

 earlier publication^* in which it was approached from the cyto- 

 genetic side. The same general principles that underlie the classi- 

 fication of individual organisms into species must apply mutatis 

 mutandis to the classification of species into genera. In other 

 words, just as species are natural groups of individuals, so genera 

 are, or should be, natural groups of species. The criteria of re- 



• Superior figures refer to items in the bibliography at the end of this essay. 



[9] 



