TREES AND SHRUBS 151 



7. HYMENOCLEA Torr. & Gray. 



Tall deciduous-leaved shrub, 6 to 8 feet high, with yellowish- 

 brown somewhat stringy bark and linear-fi iform yellowish-green 

 leaves, alternate, but often appearing fascicled, and terminal panicles 

 of rather inconspicuous dull brown heads of flowers; flowers uni- 

 sexual, the two kinds intermixed or the pistillate ones in the lower 

 axils, the staminate involucre of several united bracts, saucer- 

 shaped, the involucre of the solitary pistillate flower ovoid or fusi- 

 form, beaked at the apex and the lower part furnished with 9 to- 

 12 dilated and silvery-scarious persistent transverse wings; achenes 

 turgid, without pappus. 

 A r:ngle species. 1. H. monogyra. 



8. FLOURENSIA DC. Blackbrush 



Almost glabrous resiniferous much branched shrub, 2 to 3. 

 feet high with alternate entire leaves, eorymbous or paniculate heads 

 of flowers on short peduncles from the axils of the upper leaves; 

 flowers all tubular, no rays, yellow; receptacle flat, with scarious 

 chaff conduplicate around the compressed, callous-margined very 

 villous achenes; pappus a more or less persistent subulate awn from 

 each angle of the truncate achene and commonly some smaller ones 

 between. A single species in our range. 



1. F. cernua DC. 



9. PARTHENIUM L. Mariola 



Perennial or .sometimes annual caulescent herbs, or shrubs;, 

 leaves alternate, blades toothed, pinnatifid or dissected ; heads radi- 

 ate, but not conspicuous; involucres hemispheric, campanulate, or 

 flat, peduncled; bracts in 2 to 3 series, appressed, obtuse; receptacles 

 convex or conic, chaffy; ray-flowers usually 5, pistillate, fruit-pro- 

 ducing; ligules broad, very short, white or whitish; disk-flowers per- 

 fect, not fruit-producing, embraced by the bractlets: anthers entire 

 at the base; achenes- flattened, margined, keeled on the inner face, 

 tipped with the persistent ray-flower. 



Only one species occurs within our range. The nearly related 

 Guayule P. argentea occurs just south of us, but several attempts, 

 to grow it here have failed. 



1 P ivranum. 



