8 



As the sequence of species adoi)tecI iu this revisiou is somewbat 

 artificial, a brief discussion of tbeir apparent natural relationships is 

 here inserted. Most of the North American species can be arraugecl 

 into five rather well-defined groups, represented, respectively, by C. 

 neglecta, C. canadensis, C. purpurascens, C. aleutica, and G. deschami)- 

 sioides. 



The first group is the most strongly European in its affinities. The 

 following diagram indicates the relationships and possible genealogy 

 of its members, the length of the connecting lines measuring to some 

 extent the closeness of the relationship : 



micrantha htxiflura 



\ I 



alaskana neglecta 



californica 



crassif/himis Injperhorea inexpanun 



labradorica 



hreviseta 



The second group is possibly derived from the neglecta type, although 

 the probable line of descent is obscure. This group, like the first, is 

 closely related to European and northern Asiatic tj'pes. 



macoitiiia)i(i 



I 

 nemoralis — canadensis — langsdorffii 



I I \ 



porteri hlanda scrihneri 



The third group is perhaps derived from the neglecta type through 

 C. Jiyperhorea. It is significant that both C. inirpuraseens and C. hyper- 

 horea are found in North America and, elsewhere, only in Greenland, 

 and are apparently the only species with such distribution. Th^ pur- 

 purascens allies are related to the European C. si/Jvatk-a, but are other- 

 wise more nearly an endemic tyjje than are the two preceding groups. 



moutaiieiisis 



I 

 iweedyi iTRruKASCEXS — raseyi 



I 

 hoivelUi — foliosa 



The fourth grouj) contains two well-defined series of species, the first 

 nearly related to C. aleutica, the second to C. sulsdorfii. Through the 

 second series this group is connected with C. jHO'»>w>-a6ce«6^ and its 

 allies. Both types are ]>urelj' endemic. 



scopulunnn 



cusickii cninusta koelerioidcs 



I I ■ I 



.SUKSDORFIl ALECTICA — vUfd'f'ormis 



I I 



riibctcenn siibflexiiom 



I 

 fasciciilatn 



