320 GENTJS ATRIPLEX. 



ters by isolation. Much more intensive field studies will be necessary before this can 

 be determined. In this connection it must be pointed out that, although each plant usu- 

 ally can be placed in one or the other of the subspecies, this is done by ignoring a small 

 number of bracts which may come closer in characters to those of the other form. Some- 

 thing of the variation found on single plants is indicated in plate 49. When bracts of 

 the sonorae type occur on plants with typical barclayana bracts, the latter fall off much 

 more easily in the press, indicating an earlier maturity. 



ECOLOGY AND USES. 

 Atriplex barclayana grows commonly in the sandy or gravelly soil of back-strands 

 and of alluvial fans at the mouths of canons, as well as on dunes. It also grows inland 

 in gravelly washes, always preferring soil that is slightly or not at all saline. In all such 

 situations it occurs as a scattered secondary species. However, on the guano islands of 

 the Gulf of California, where the soil is discolored with guano salts, it is a dominant, 

 usually associated with Amarantus watsoni, which is equally important. These two 

 species constitute the initial associes, which forms 95 per cent of the vegetation of such 

 islets. Nothing is known of the uses of this species. 



36. ATRIPLEX ACANTHOCARPA (Torrey) Watson, Proc. Am. Acad. 9:117, 1894. 

 Plate 50. BuRSCALE. 



Erect subshrub or herbaceous perennial with a woody base, 1 to 10 dm. high, freely 

 branched from the base; branches stout, obtusely angled or nearly terete, densely fur- 

 furaceous or those of the staminate plants nearly naked, glabrate in age, the bark exfol- 

 iating in layers from the old woody portions ; leaves mostly alternate but the lower ones 

 opposite, tapering to a short- or long-winged petiole, varying from lanceolate to oblong- 

 elliptic or obovate, narrowed at base, obtuse at apex, 2 to 5 cm. long, 0.5 to 2.5 cm. wide, 

 more or less sinuate-dentate or some of the leaves entire, rather thick or thinnish, white 

 with a dense and permanent scurf; flowers dioecious, the staminate in glomerules along 

 the branches of elongated nearly leafless terminal panicles, the pistillate in more leafy 

 panicles or racemes; perianth 5-cleft in the staminate flowers, wanting in the pistillate; 

 fruiting bracts on stalks 2 to 20 mm. long (or a few subsessile), thick and spongious, 

 united nearly to the apex, subglobose or broadly elliptic in outline, 8 to 14 mm. long and 

 nearly as broad, the free tips often beak-like, the faces bearing numerous flattened, irreg- 

 ular, often toothed appendages, these commonly longer than the body; seed 1.5 to 2 mm. 

 long, brown; radicle superior. {Obione acanthocarpa Torrey, Bot. Mex. Bound. 183, 1859.) 



Western Texas to southern Arizona, Chihuahua, and San Luis Potosi. Type locality, 

 plain between the Burro Mountains, New Mexico. Collections: Guadalupe, 105 miles 

 southwest of San Antonio, Texas, Palmer 1167 (Gr); "western Texas to El Paso, New 

 Mexico," Wright 57S (Gr, NY, IJS); Franklin Mountains near El Paso, Texas, Rose 

 17891 (NY, US); banks of the Gila River, New Mexico, August, 1880, Greene (Gr); 

 Winslow, Arizona, Jones 102 (Gr); vicinity of Torreon, Coahuila, Palmer J^7S (Gr, NY, 

 UC, US); southwest of Parras, Coahuila, Palmer 1161 (US); Sapio, Sierra Madre Moun- 

 tains, Chihuahua, September 10, 1903, Jones (US); Chihuahua State, Hartman 723 (Gr, 

 NY, UC, US) ; alkaline plains, Hacienda de Angostura, San Luis Potosi, Pringle 3775 (Gr, 

 NY, UC, US, type collection of A. pringlei Standley, minor variation 2). 



MINOR VARIATIONS AND SYNONYMS. 



1. A peculiarly slender-stemmed and thin-leaved form has been collected in Texas and New Mexico. 

 The stems in this are but obscurely farinose and even the leaves are only thinly covered with scales and there- 

 fore greenish. The absence of complete fruiting specimens would render taxononiic recognition impossible 

 at this time, even if it could be demonstrated that the form is other than an ecad. Representative collections 

 are: southwest of San Antonio, Texas, Palmer 1157 (US); New Mexico, Wright 1737 (US). 



