The Genus Achillea in North America "^ 



Bv Chakles Lol'is Tollard. 



This genus, as now generally understood, consists of from 

 eighty to one hundred species, confined almost entirely to the tem- 

 perate regions of the Old World. Its critical study has been ne- 

 glected by American botanists, owing probably to the fact that its 

 representation on this continent was believed to be restricted to two ■ 

 or three species, even these being supposedly introduced from 



abroad. 



The Tournefortian genus Ptarniica^ which was accepted by De 



Candolle in the Prodromus, has usually been regarded as scarcely 

 more than a subgenus o{ AcJiillca. The heads of both are radiate 

 as well as discoid, and in both the achenes are more or less mar- 

 gined. The chief points of distinction lie in the shape of the in- 

 volucre and the degree of convexity which the receptacle exhibits, 

 while there are few or no habital differences. In this paper, there- 

 fore, Achillea is accepted as outlined by Hoffman in *' Die natiir- 

 lichen Pflanzenfamilien.'' 



■ 



It is an odd coincidence that the type species of both PtaiDiica 

 and Fjiachillca should occur in North America. A, Ptarniica L. 

 is introduced in various portions of the northeastern states, and 



also in Newfoundland and British Columbia 



iMilhfoliuin 



the familiar yarrow, occurs likewise as an introduced weed in 

 meadows, pastures, etc., throughout the Atlantic states from Nova 

 Scotia to Florida, and westward to the Rocky Mountains ; it is 

 also occasionally found on the Pacific coast. The fact, however, 

 that the yarrow, of one form or another, extends not only through 

 the West, but northward as well through British Columbia and 



has induced most botanists 

 e plant a circumpolar type 



Alaska, and southward into Mexico, 

 of the present century to consider the plat 

 with a well-nigh world-wide distribution. Yet from the earliest 

 pilgrimages of western pioneers, long before the region was pene- 

 trated by railroads, Achillea has been equally as abundant, and 

 equally at home under conditions that absolutely preclude the as- 



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■^rviblished by permission of the Secretary of the Smithsonian Institution, 



(3(35) 



