A. ABROTANUM. 49 



Section I. ABROTANUM. 

 Phylogeny of the Species. 



There are two native North American species in this section which are so isolated 

 phylogenetically from the others that they are represented on the chart by divergent 

 lines from the base. One of these is A. calif ornica. This is similar to two Old World 

 species now introduced into the United States, A. abrotanum and A. pontica, but since 

 the connections may be rather remote these are indicated by broken lines. The other 

 isolated native species is A. bigelovi, which may have arisen from A. calif ornica, but is 

 probably of more ancient lineage. The remaining species fall into three natural assem- 

 blages, conveniently referred to as the norvegica, vulgaris, and biennis groups. 



The norvegica group, that is, those species inclosed in a major circle at the left, is 

 certainly of boreal origin, norvegica itself having a more or less continuous distribution 

 in the circumpolar regions of Eurasia and North America, with a southward extension 

 into the Rocky Mountains. The center of distribution was probably in Siberia, the 

 American forms coming by way of Alaska and thence down the continent. A. parryi 

 is a stranded species of high mountains near the southern limits of the group, while 

 macrobotrys and senjavinensis are boreal developments that do not extend far southward. 



The vulgaris group is not inclosed in a major circle on the chart because the species 

 are not so closely related to one another as are those of the other two groups. A. vulgaris 

 itself is of wide distribution on both continents, has its center of distribution in northern 

 Asia, and has a fan-like distribution in North America, the area of widest extent east 

 and west being in the United States. In the course of its migrations this species has 

 adapted itself to an extensive series of conditions, and an enormous number of minor 

 variations and subspecies has resulted. The northern broad-leaved, large-headed tilesi 

 undoubtedly represents the most primitive of these, since the others exhibit increasingly 

 specialized structures when arranged in the order of their southerly and easterly distri- 

 bution. The other species of the vulgaris group are stelleriana, which is of wide distri- 

 bution but restricted to sandy beaches; alaskana, a little-known species of the far north; 

 and franserioides, which apparently is a relict stranded in the southern Rocky Mountains. 



The biennis group comprises three species, all closely related and characterized by 

 their annual or at most biennial habit. Two of the species are represented also in Europe, 

 and since none of them occur in Arctic regions, it seems probable that they have reached 

 America by way of the North Atlantic, where land connections may have been more 

 recent than across the Pacific, or it may be that the introduction was even more direct. 

 Whatever the route, the connection is an old one, since time must be allowed for the 

 later evolution of the peculiar Mexican A. klotzschiana. 



The evidence upon which this sketch is based is indicated in detail in the paragraphs 

 on the relationships of the several species. 



1. ARTEMISIA ABROTANUM Linnaeus, Sp. PI. 845, 1753. Plate 1. Garden 



Sagebrush. 



A shrub, 5 to 20 dm. high, pleasantly scented; stems much branched, erect or some- 

 what spreading, forming rounded bushes, the twigs erect, prominently striate, glabrous, 

 often red or reddish tinged; principal leaves numerous, petioled (petiole naked at base), 



3 to 6 cm. long, 2 or 3 times pinnately dissected into ascending linear-filiform divisions 

 with revolute margins, green, glabrous or sparsely puberulent above, lightly tomentulose 

 beneath; upper leaves similar but smaller and some only once pinnatifid or 3-cleft or 

 entire; inflorescence an elongated terminal panicle, leafy below, 15 to 40 cm. long, 



4 to 15 cm. broad; heads heterogamous, short-peduncled, nodding; involucre hemispheric 

 or subglobose, about 2 to 2.5 mm. high, 2.5 to 3 mm. broad (involucres somewhat larger 

 according to some descriptions, but only small-headed forms thus far seen) ; bracts 8 to 



