iqis] SHERFF— BIDENS 305 



having achenes sometimes approaching those of Cosmos and with 

 rays varying, in herbarium specimens, from yellow to white, rose, 

 or violet (a single sheet frequently showing all these variations, as, 

 for example, Palmer 674, Herb. Kew). 



During the past few years, certain writers, notably Oliver 

 and Hiern, S. L. Moore, and 0. Hoffmann, have described a con- 

 siderable number of striking and positively new species of Coreopsis 

 and Bidens from various parts of Africa. In their generic dis- 

 tinctions, however, they have unfortunately been guided mainly 

 by the direction of the barbs on the awns of the achenes, or, in cer- 

 tain cases, they have had access at the time to immature achenes 

 only. Regarding the latter point, the disadvantage and source 

 of error are at once evident on examining the real distinctions be- 

 tween Coreopsis and Bidens. As will be seen below, the presence 

 of two more or less conspicuous lateral wings upon the achenes 

 seems by far the most nearly constant character of Coreopsis as dis- 

 tinguished from Bidens. But in several species of Coreopsis these 

 wings are completely lacking on the immature achenes. Thus, 

 species described from immature specimens as Bidens may later 

 prove to be Coreopsis. Again, a species erroneously described from 

 immature specimens as Coreopsis, because of a recognized resem- 

 blance to some particular species of Coreopsis and disregarding the 

 absence of wings, must thereafter be treated by botanists as Core- 

 opsis until mature material can be obtained to prove its status as 

 true Bidens. 



Concerning the direction of the barbs on the awns of the achenes, 

 however, a more detailed statement is needed. Until compara- 

 tively recent times, botanists referred to Bidens those species with 

 retrorsely barbed awns, and to Coreopsis those species with an- 

 trorsely barbed awns or with awns inconspicuous. But, from time 

 to time in North America, new forms have been discovered, iden- 

 tical in each case with a certain species of Coreopsis (as then de- 

 limited) or Bidens except in the direction of the barbs on the awns. 

 Asa Gray (cf. Fernald, Rhodora 15:77- 1913), when confronted 

 with such a form of " Coreopsis aristosa Michx." (the then accepted 

 name), designated it "C. aristosa in Bidentem transformata." 

 Later (Synop. Fl. N. Amer. 1": 294-296. 1884) he treated this 



