192 



GENUS CHRYSOTHAMNUS. 



long bracts to filifoUus. This is useful in that it calls attention to the fact that this 

 narrow-leaved, small-headed form has a more compact inflorescence than typicus. 

 However, the individual heads in the latter are also sometimes sessile (for example, 

 Purpus, 6264), while the variation in the length of the subtending bracts does not vary- 

 in unison with other characters. Since the two forms occupy the same general terri- 

 tory, careful field observations should be made to see if they are not entirely ecologic 

 in their origin. 



Table 19. — Vartation in the subspecies of Chrysothamnus greenei. 



' Type of Chrysothamnus greenei Gray, 



' Type of C. acoparius Rydberg, minor variation 5. 



' Type of C. pumilus acumiTmtus Nelson, minor variation 4. 

 ' Type of C. filifoUus Rydberg = C. greenei filifoUus. 



ECOLOGY AND USES. 



Chrysothamnus greenei is a low shrub, blooming during August and September. It 



forms a climax society in mixed prairie in the San Luis Valley, Colorado, while in Utah 



it sometimes forms a subclimax consocies on sandy alkaline plains. It is greatly increased 



by overgrazing, and hence is frequently associated with Bouteloua gracilis in short- 



There is no specific information at hand regarding the value of this plant. As a browse 

 shrub it is probably of about the same value as the smaller subspecies of C. tnscidiflorus. 



7. CHRYSOTHAMNUS ALBIDUS (Jones) Greene, Erythea 3 : 107, 1895. Plate 28. 

 Shrub 3 to 10 dm. high, fastigiately branched; twigs brittle, erect, congested, very 

 leafy, glabrous but very resinous-viscid, imparting a resinous stain to paper, at first 

 green and striate, later with a white smoother bark; leaves flat and 1 to 2 mm. wide 

 but drying to filiform through revolution of the margins, pungently acute, 2 to 4 cm. 

 long, 1 -nerved, moderately rigid, glabrous but with a copious resinous exudate, the 

 surface with small pits ; heads in small congested cymes which are either simple or them- 

 selves loosely cymose; involucre 7 to 9 mm. high; bracts about 15, in very obscure 

 ranks, lance-oblong, all but the innermost abruptly narrowed to a long setiform usually 

 curved tip, glabrous, glutinous, the thin margins somewhat erose, the tip sometimes 

 herbaceous; flowers 5 to 6 (whitish or at least pale yellow); corolla with slender tube 

 and abruptly dilated short throat, 7 to 8 mm. long, glabrous; lobes linear, acute, 2 

 to 2.5 mm. long, erect; anther-tips triangular, obtusish, 0.2 mm. or less long; style- 

 branches exserted, the slender appendage (about 2 mm. long) much exceeding the short 

 stigmatic portion (0.5 to 1.0 mm. long); achenes tapering to the base, about 4 mm. long, 



