446 EQUISETACE^E. (HORSETAIL FAMILY.) 



4. E. robustum, Brauu. Stems 3 to 6 feet high; the ridges narrow, rough 

 with one line of tubercles : sheaths short, with a black girdle above the base, 

 rarely with a black limb, and about 40 deciduous 3-keeled teeth with ovate-awl- 

 shaped points. From British America to Mexico, and extending eastward to 

 Louisiana and Ohio. 



5. E. hiemale, L. Stems l to 4 feet high ; the ridges roughened by two 

 more or less distinct lines of tubercles: sheaths elongated, with a black girdle 

 above the base and a black limb, of about 20 (17 to 26) narrowly linear teeth, 

 l-keeled at the base and with awl-shaped deciduous points. In Utah and Wyo- 

 ming, to British America and the Atlantic States. The " Scouring Rush," or 

 ' Shave Grass." 



i- -i- Stems slender, in tufts, 5 to 10 grooved, sheaths looser. 



6. E. variegatum, Schleicher. Stems ascending, 6 to 18 inches long, 

 usually simple from a branched base, 5 to IQ-grooved: sheaths green variegated 

 with black above; the 5 to 10 teeth tipped with a deciduous bristle. Clear 

 Creek, Colorado ( Coulter), Utah, and Wyoming ; also in the Atlantic States 

 and northward. 



7. E. SCirpoides, Michx. Stems very numerous in a tuft, filiform, 3 to 6 

 inches high,Jle,xuous and curving, mostltj 6-grooved, with acute ridges: sheaths 

 3-toothed, the bristle-pointed teeth more persistent. Utah and Wyoming ; 

 also in the North Atlantic States and northward. 



