distinctly 3-nerved; heads in a terminal corymbiform aggregation, often on several 

 branches; pistillate heads with about 50 flowers or more; involucre hemispheric, 

 about 4 (-4.5) mm. high; phyllaries ovate or lanceolate, obtuse (inner may be 

 acute), stramineous, brown-purplish-tipped, the midrib distinct with its margins 

 scarious and erose; receptacle flat, nearly smooth, naked; corolla filiform, 2-2.3 

 nirn. long, with 5 narrow linear lobes 0.2 mm. or less in length; style exserted, 

 bifurcate; pappus uniseriate, flaccid, 4-5 mm. long; achenes about 1 mm. long, 

 glabrous, 5-ribbed; staminate heads 10- to 20-flowered; involucre campanulate, 

 about 4 mm. high; phyllaries ovate-lanceolate, obtuse to acute, marginally scarious 

 and erose; receptacle flat, slightly pitted, naked; corolla 3-4 mm. long, filiform, 

 upper half funnelform, its 5 lobes lanceolate and about 1.2 mm. long; pappus 3-4 

 mm. long, plumose-tipped, crisped, not exceeding corolla; ovary abortive. 



Along sandy watercourses in dry areas, often forming thickets along the Rio 

 Grande, in the Trans-Pecos, Edwards Plateau and Rio Grande Plains, Tex., in 

 N. M. (widespread, in river valleys), and Anz. (common along watercourses), 

 Mar.-Dec; widespread in Am., n. to Calif., Colo, and Tex. 



S. Baccharis viminea DC. Mule-fat. 



Shrub; branchlets glabrous or glandular; leaves crowded, punctate, narrowly 

 elliptic, entire to minutely serrate, tapering acutely at both ends, 3-5 cm, long, 

 5 (-10) mm. wide, 1 -nerved with 2 indistinct lateral nerves narrowly paralleling 

 the margin; heads in small corymbiform aggregations terminating numerous lateral 

 branches; pistillate heads with 50 or more flowers; involucres campanulate to 

 semi-hemispheric, about 4 mm. high; phyllaries ovate to lanceolate, obtuse to 

 acute, stramineous to brown-purplish-tipped, scarious-margined and erose; recep- 

 tacle flat, smooth, naked; corolla filiform, with 5 small lobes; pappus uniseriate; 

 achene glabrous; staminate heads with about 20 flowers; mvolucres broadly 

 hemispheric, about 3 mm. high, to 5 mm. thick; phyllaries ovate to lanceolate, 

 obtuse to acute, marginally scarious and erose; receptacle flat, naked; corolla tube 

 filiform, the limb funnelform, with 5 lanceolate lobes; pappus 3 mm. long, 

 plumose-tipped, crisped; ovary abortive. 



Along washes and floodplains of streams, rare and local near El Paso, Tex., 

 through N.M. to Ariz. (Yavapai and Yuma cos.), spring-summer; Baja Calif., 

 Calif., Wash., Ariz., N.M. and Tex. 



7. Xanthocephalum Willd. Broomweed. Snakeweed 



An American genus of perhaps 30 species. 



Some of the species are extremely common weeds that increase enormously 

 under the prevalent regime of abusive overstocking. The herbage of several species 

 is known to be toxic to livestock. The annual species are called "broomweed" 

 and the shrubby species "snakeweed." 



Ic Xanthocephaliim gymnospermoides (Gray) Rothr. 



Stout annual to 2 m. tall; branchlets often with stipitate glands; leaves alternate, 

 lanceolate, 3-15 cm. long, 5—30 mm. broad, glabrous, with entire or serrate 

 margins, acute, above shiny and somewhat glutinous; heads solitary at the ends 

 of the branchlets but clustered in subcymose aggregations; involucre campanulate, 

 glutinous, 3-7 mm. thick, 3-6 mm. high; phyllaries numerous in 2 loose series, 

 glabrous, appressed, usually with green midrib and tips, apically spreading; 

 receptacle flat or slightly convex, alveolate; ray flowers pistillate, 50 to 70, the 

 yellow rays 2-4 mm. long and 1-1.5 mm. broad, about the same length as the 

 tube; disk flowers 150 to 200, 2 to 3 times as many as the ray flowers; corolla 

 about 4 mm. long, with a narrow tube and expanded throat; style with pointed 

 collecting hairs and these restricted to the short deltoid tips; pappus in some plants 



1608 



