A. NUTTALLI. 327 



whiter tomentum, but nonn of these features are sufficiently well-marked to be of service in distinguishing 

 this from true nuttalli. Type locality, Delta, Colorado. 



15. A. PABULARI8 Nelson, Bull. Torr. Club 25: 203, 1898.— A. nuUalli tridenlata. This is a forna with 

 crowded strictly erect leafy stems clustered on a very short woody base, the branches of which are slightly 

 spreading. Thus the plants come to form close rounded tufts. TIk- bracts are about as in typical triderdcUa but 

 some of them tend to be broadest toward the summit, thus approaching subspecies gardneri (fig. 46). At 

 the type locality, namely. Point of Rocks, Wyoming, some plants with the habit of pabidaris have bracts so 

 broad above that thoy are referred to subspeci(^s gardneri (Hall 10936). Aa far as known the pabidaris form 

 is confined to highly alkaline clays of low flats immediately adjacent to saline streams. 



16. A. PAHULAuis EREMicoLA Nclson, in Coulter and Nelson, Man. Rocky Mt. Botany, 168, 1909. — Based 

 upon A. eremicola Ostcrhout, which see. 



17. A. TuiDENTATA Kuntzc, Rcv. Gen. PI. 546, 1891. — A. nuttalli tridentata. 



18. Odione GARDNERI Moquin, in De CandoUe, Prodr. 13': 114, 1849. — A. nuttalli gardneri. According 

 to both the International and American Codes this form should be taken as the type of the collective species, 

 the name of which would then become Atriplex gardneri (Moquin) Standlcy. Under this arrangement all 

 of the subspecies here assembled would be transferred to A. gardneri. The reasons for retaining A. nnUalli as 

 the inclusive name are that it has become well established in the literature, that its typical form is abundant 

 and well-known to botanists, and that if the other name wore adopted there would still remain a difference of 

 opinion as to whether or not it should be corrected to gordnni, as proposed by Hooker (Jour. Bot. and Kew 

 Misc. 5:261, 1853). 



RELATIONSHIPS. 



Atriplex nuttalli belongs to a small group of dioecious species which stand intermediate 

 between the herbaceous and the truly shrubby forms. Its derivation doubtless was from 

 a Mexican stock, which yielded also such semi-shrubby species as A. barclayana, A. 

 acanthocarpa, and A. obovata. In the process of its northward migration it left these 

 forms behind, both geographically and phylogenetically, so that it has now come to 

 inhabit the alkaline plains and slopes from the southern Rocky Mountains and Great 

 Basin northward and has developed a combination of essential characters not found in 

 any of the others. The only related species which grows well within its area is A. 

 corrugata, a still less shrubby form with its own peculiar characters, as will be later 

 indicated. 



In the process of establishing itself in the extensive area now occupied, the original 

 nuttalli stock diverged into several subspecies and a large number of minor variations. 

 All of these are so closely held together by intermediate forms that the separation into 

 district species is impracticable. Standley's 8 species, diagnosed in the North American 

 Flora, are based upon features which field study and the abundance of recent collections 

 have demonstrated to be unstable. The only one which stands out distinctly over most 

 of its area is falcata. This is based upon its narrow fruiting bracts, and, although 

 exact intermediate forms have not as yet been found, the character is of such a nature 

 that it may be expected to vary. Jones, the original sponsor of falcata, gave it varietal 

 rank under nuttalli. 



The first three subspecies form a very close group, and since they occupy the same 

 region, it is questionable if all should not be treated as one. But the peculiar bracts 

 of subspecies gardneri are quite distinctive in the extreme form, being decidedly broadest 

 above and with margins uniformly narrowed toward the base. The bracts are thus 

 cuneate-oblong with a truncate summit. However, the sides are sometimes so nearly 

 parallel that it is difRcult to say whether the bracts belong to this or to subspecies triden- 

 tata (e. g., in Nelson 3667 from Sweetwater County, Wyoming, and in Hall 10935 and 

 Nelson 4429, both from Point of Rocks, Wyoming, the latter the type of A. pabularis 

 Nelson, minor variation 15). A few of the shapes are shown in figure 46. The two 

 subspecies of this group with bracts broadest below, i. e., lypica and tridentata, differ 

 from each other in habit as well as in the characters used in the chart. The latter is the 

 less woody at base and the strictly erect stems form a close, almost columnar plant. 

 The tendency toward the absence of appendages on the bracts is tentatively employed 



