446 EQUISETACE^. (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-Jceeled 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." 



•»- •*- Stems slender, in tufts, 5 to lO-grooved, sheaths looser. 



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

 usually simple from a branched base, 5 to \Q-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, filexuous and curving, mostly 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. 



