The Origin of Crepis and Related Genera 25 



ber of flower heads, and reduction in length of the hfe cycle, the 

 endemics can be classified roughly as "old" or "young!' The 

 former category obviously includes the more primitive species 

 or relics, and the latter contains the comparatively recent ones. 

 In all three subgenera about one-third of the endemics appear 

 to be old species. Thus the proportions of endemics and of relics 

 in the subgenera is in harmony with the conception that Catonia 

 is the most primitive, Bar^hausia the most recent, and Eucrepis 

 intermediate. 



The geographical distribution of the subgenera is in general 

 agreement with this conception. As is shown in figure 3, Catonia 

 occupies most of Europe, Asia, and Africa, but does not occur in 

 the New World; Eucrepis covers about the same area in the Old 

 World except that in Africa it is represented only in the north 

 and northeast, but it is also found in western North America 

 and in a few localities in Labrador and Newfoundland; Bar\' 

 hausia is restricted to the Mediterranean region and adjacent 

 areas. It is significant that Eucrepis, which has the widest dis- 

 tribution, contains twice as many species as either of the other 

 subgenera and is more complex in its difiFerentiation into mor- 

 phologically distinct subgroups. It will be shown below that 

 these evolutionary features are associated with greater variability 

 in chromosome numbers and chromosome morphology in Eu- 

 crepis. The phyletic relations between the three subgenera are 

 summarized in figure 4. 



The somatic chromosome numbers found in the Old World 

 species of Crepis are 6, 8, 10, 12, 14 (15-24), 16, and 40, while 

 the North American species have 22, 33, 44, 55 ( ?), and 88 {}), 

 besides 14 in two representatives of an Old World group. In 

 figure 5 the distribution of these numbers in the subgenera is 

 shown by indicating as exponents the numbers of species known 



