The Origin of Crepis and Related Genera 41 



some numbers, we find three groups, namely, those with 12 

 chromosomes, those with 14 chromosomes, and those having 

 22 chromosomes as the base number. As in the groups discussed 

 above, the position of each species in the series (fig. 10) is deter- 

 mined on the basis of comparative morphology, considered with 

 reference to geographic distribution which, in the 12-chromo- 

 some group, is as follows: mollis extends from western Europe 

 to middle Asia; lyrata is found in western Siberia; pygmaea 

 occurs only in the European Alps; montana, only in Greece; 

 mungieri, only in Crete; Willemetioides, in northeastern Persia; 

 and hierosolymitana, in Palestine, Syria and Cyprus. 



At present only three species with 14 chromosomes are known, 

 yet they comprise an even more widespread group than the pre- 

 ceding one. C nana, in fact, is the most widespread species in the 

 genus, being distributed from central Asia to eastern Labrador, 

 at high elevations in the Rocky Mountains, and in the higher 

 ranges of Utah, Nevada, and the Pacific Coast states. C. elegans 

 occurs only in Alaska and the Rocky Mountains, and C. flexuosa 

 is distributed from Outer Mongolia and Semipalatinsk to the 

 Altai and Himalaya mountains. 



The remaining Eucrepis species occur only in North America. 

 As is indicated in the chart (fig. 10), there is good evidence to 

 support the hypothesis that all these species with 22 as the base 

 number originated through hybridization between 14-chromo- 

 some and 8-chromosome species followed by amphidiploidy. 

 The region of origin is uncertain, but it seems most probable that 

 it was in southern Alaska or an adjacent area to the south, and 

 that the progenial species did not survive the subsequent glacial 

 epoch in which their more vigorous offspring were able to mi- 

 grate southward. At any rate, the distribution of these exclu- 

 sively American species indicates a radiation from southwestern 



