The Origin of Crepis and Related Genera 19 



logically. Nevertheless, it does not seem probable that any other 

 genera in the Crepidinae will be found to be more closely re- 

 lated to Crepis than these. (Two small genera, Pterotheca and 

 Rodigia, both having 5 as the haploid number, are merged with 

 Crepis by the author.) Reference again being made to the evi- 

 dence from chromosome numbers, the marked divergence of 

 Crepis, Paraixeris, Crepidiastrum, and Chondrilla from the other 

 genera represented in figure i, may point to certain evolutionary 

 processes underlying the differentiation of these and perhaps 

 other genera in the Cichorieae. As will be shown below, our 

 present knowledge of Crepis makes it possible to advance a 

 tentative hypothesis concerning the nature of these processes. 



The evidence from geographical distribution supports the con- 

 ception of a common origin for Crepis and its allies. If the dis- 

 tributional areas of the three largest genera are compared, it is 

 found that they all include most of Eurasia and at least part of 

 Africa (fig. 2). All the other genera which have been studied 

 cytologically occur in this same geographical unit. This suggests 

 a common origin for these genera, and the distribution of the 

 more primitive types of Crepis and its allies indicates that the 

 region of common origin is south-central Asia. Additional evi- 

 dence will be presented in the second and third parts of this 

 paper. 



The fact that Hieracium is so widely distributed might at first 

 seem to indicate that it is therefore the most ancient. But this is 

 not necessarily true, because certain unique features of this great 

 genus are sufficient to explain its present large spread over the 

 earth's surface. According to Zahn,*' there are numerous species 

 of Hieracium which are intermediate between other principal 

 species; these "Zwischenarten" often produce numberless prog- 

 eny and sometimes considerably transgress the distributional 



