C. NAUSEOSUS. 229 



known shrub of eastern Arizona. It is usually described as cinereous, or minutely 

 canescent, but the twigs, even in the type, have the usual pannose tomentum. Sub- 

 species turhinatus, also a rare plant, known only from Utah, is more striking because 

 of its elongated, cylindric involucres, but no character can be found as a basis for a 

 distinct species. The original description reads "plants glabrous and a little glutinous 

 even to the flowers." The type collection and two others have been examined. In all 

 of these the copious tomentum of the twigs is so closely packed that it gives the appear- 

 ance of a glabrous surface, the leaves are tomentulose, and the corolla-lobes hairy. 

 Junceus and turhinatus are similar not only in the points mentioned, but also in habit 

 and distribution. They appear to form an offshoot which sprang from the main stock 

 at an early stage in the development of the genus. Their close connection with sub- 

 species glareosus and leiospermus is evidenced by the variable nature of the pubescence 

 on the corolla-lobes, by the erratic occurrence of this in bigelovi (see p. 167), and by transi- 

 tions between glabrous and pubescent achenes, as will be indicated under leiospermus. 



The last group to be considered is the one with glabrous achenes. The three sub- 

 species that comprise it all come from the arid southerly portion of the Great Basin 

 and are sufficiently alike in essential characters to lead to the conclusion that the group 

 is probably a natural one. The absence of pubescence on the achenes is not of specific 

 taxonomic significance, as is indicated by collections of leiospermus made near Caliente, 

 Nevada (Hall 10791, 10795). In some of these plants the achenes are very sparsely 

 pubescent on the edges, in others they are sparsely pubescent both along the nerves 

 and on the intervening spaces. At this station the conditions are extremely xerophytic. 

 This is reflected in the plants, which are quite leafless, thus resembling those of junceus 

 in appearance. There is considerable variation in the color of the tomentum in leio- 

 spermus. The first specimen cited under the original description has twigs that are white 

 in the inflorescence and for a distance of about 1 dm. below the heads, while from there 

 down they are yellowish-green; in the other specimen cited the twigs are very white 

 down to the old wood; in more recent collections, such as those from Caliente, Nevada, 

 the twigs are green throughout. The subspecies glareosus and higelovi differ from 

 leiospermus not only in their pubescent involucres, but in matters of habit, in the more 

 definite ranks of the bracts, and in the greater length of the involucre. All of these last 

 five subspecies inhabit the southern part of the Great Basin. They have been greatly 

 modified, especially in habit and foliage characters, and these modifications enable them 

 better to cope with their very arid and often alkaline habitat. 



ECOLOGY. 



In general, the important subspecies of Chrysothamnus nauseosus are subclimax 

 dominants of the sagebrush association. Forms of graveolens are abundant in the western 

 portions of the mixed prairie, and of speciosus in particular in the bunch-grass prairie 

 of the Northwest. They extend northward into Canada, but are found in the drier 

 parts of the Southwest only in valleys in the mountains. As a rule, they mix and alter- 

 nate with the sagebrush, except for such halophytes as consimilis and viridulus, which 

 often form pure stands on alkali flats below it, in association with Distichlis and Iva 

 axillaris. The pinifolius form of graveolens is also frequently halophytic, when it grows 

 in mixture with Sarcobatus. All of these are serai dominants, and with drainage or 

 shifting climate yield to the subclimax dominants, such as speciosus, gnaphalodes, 

 hololeucus, albicaulis, etc. Graveolens is characteristic of the cliff edges and gullies of 

 the bad lands of western Nebraska and the Dakotas. 



This species reproduces readily from seed, and grows vigorously when transplanted, 

 even when the crowns are divided. It forms basal sprouts after cutting, but only rarely 

 when burned. Most of its forms are among the latest bloomers of the genus, the flowers 

 appearing in September and often continuing into December. 



