126 GENUS ARTEMISIA. 



RELATIONSHIPS. 



The species of Artemisia most closely connected phylogenetically with A. campestris 

 are natives of Asia or possibly of Europe. Of these, A. commutata Besser is so close that 

 it should be merged into it, as has been already done by some. As a subspecies, or series 

 of subspecies, for it passes into numerous forms similar to those occurring in America, 

 commutata stands between typica and the other perennials described above. Its distribu- 

 tion from the Caucasus to Baikal and Davuria, in Siberia, together with its trait of 

 breaking up into forms similar in character to ours, suggests that it may represent the 

 ancestral strain which, crossing the Bering Straits, has given rise to at least some of the 

 American subspecies. A coordination between the Siberian and American forms is 

 impossible at the present time from a lack of field knowledge. Another Siberian species 

 of close relationship is A. desertorum Sprengel, to which several of the American forms 

 were once assigned by Besser. This has all of the essential characters of campestris, but 

 is perhaps to be retained because of its much wider leaf-segments. The only American 

 Artemisia closely allied to campestris is A. dracunculus, and even here the separation 

 probably took place in the Old World. There is no constant floral difference between the 

 two, but the much more pronounced segmentation of the leaves and the tendency to 

 produce most of these in a basal rosette give to campestris a very different aspect. 



In taking up the segregates of this cosmopolitan species it is first noted that the typical 

 form is common on the plains of Europe and western Asia. In America it is known 

 from only a few isolated stations along the Atlantic seaboard, where it is probably 

 adventive from Europe. It is a tall, perennial herb with numerous stems from the base, 

 very narrow leaf-segments, and small, ovoid heads in an open, loosely branched inflores- 

 cence. On the plains and in the lower mountains of the western States grows a subspe- 

 cies so similar that it is easily mistaken for typica. This is pacifica (often erroneously 

 referred to canadensis). In this the heads are usually broader at the same stage of 

 development, but they sometimes so closely match the heads of the Old World type that 

 the two can not be distinguished by this feature alone. The pubescence in pacifica is 

 more dense and persistent than the general run of typica, but some mature specimens of 

 the latter are densely sericeous (Lower Austria, November 3, 1898, Klebs). A. commu- 

 tata, which is not specifically separable from campestris, is said by Ledebour (Fl. Rossica 

 2:567, 1845) to vary from apparently glabrous to villous-sericeous. The most nearly 

 constant character of subspecies pacifica is its compact inflorescence, the branches of 

 which are strict and ascending, not outwardly curved as in the other. Since even this 

 distinction requires a series of specimens for its practical use, and since the other char- 

 acters are shown to be of but little moment, it now seems impossible to retain pacifica in 

 more than subspecific rank. 



The Old World type of campestris is more closely approached in size and shape of head 

 and in the inflorescence by subspecies caudata, of the eastern and central States, but this 

 is unique in the genus in having a biennial taproot and usually but a single stem, the 

 latter character perhaps a result of the biennial habit. These traits are so strikingly 

 constant that the subspecies seems possibly not to have arisen from any of the others here 

 described, but from some Old World form with which we are not familiar. Taxonomi- 

 cally it is the most distinct of all of the subspecies except pycnocephala. 



The next two subspecies, that is, borealis and spithamaea, are both of northerly dis- 

 tribution, scarcely reaching the United States except in the higher mountains. They 

 extend from Greenland to the Aleutian Islands, and borealis has its type locality in Siberia. 

 The influence of the boreal habitat is seen in the large size of the heads, in the reduced 

 inflorescence, and in the strictly perennial root. This stout root supports at the surface 

 a branching caudex from which arise several or numerous annual stems. Fundamentally 

 this is not different from the habit of typica and pacifica, but the caudex is more branched, 



