roots; aerial stems evergreen, simple or occasionally sparingly and irregularly 

 branched, frail to somewhat stout, pale-green, mostly clustered, 3-15 dm. tall, 

 to 8 mm. in diameter, longitudinally 14- to 30-grooved, with the ridges smooth 

 or slightly scabrous; sheaths elongate, dilated upward, marked with a black 

 girdle at the base of the mostly deciduous white-margined subulate brownish teeth 

 and rarely also at the base of the sheaths, with the ridges of the sheaths 1- to 

 3-keeled, the lowermost sheaths 5-12 mm. long; cones ellipsoid, sharp pointed, 

 1-2 cm. long, 7-10 mm. in diameter. 



Distinguished from E. hyemale, which it closely resembles, by its smoothness, 

 long green sheaths with a narrow black limb, and darker green color. Forma 

 scabrellum (Engelm.) Broun has more prominent cross bands of silex on the 

 ridges than in f. laevigatiim. 



In sandy soil or sandy loam along streams and lake banks, on seepage slopes, 

 in alluvial thickets, marshes, meadows, prairies, sandy barrens and rocky creek 

 beds of canyons, rather generally distributed in Okla., w. and cen. Tex., e. to 

 Somervell and Waller cos. in the Blackland Prairies and s. to Starr Co. in 

 the Rio Grande Plains, throughout N.M. and Ariz. (Navajo and Coconino, s. to 

 Cochise, Santa Cruz and Pima cos.); from Anticosti Is. and Que. to B.C., s. to 

 N.C., La., Tex., N.M., Ariz, and Calif.; also Mex. and Guat. 



4. Equisetum hyemale L. var. affine (Engelm.) A. A. Eat. Canuela, tall 



SCOURING-RUSH. Fig. 6. 



Rhizome slender, creeping, blackish, with a ferruginous tomentum covering 

 the fibrous roots; aerial stems erect, evergreen, stout, solitary or cespitose, fluted 

 with many ridges that are scabrous with bands of siliceous tubercles, to 3 m. 

 tall and 2.5 cm. in diameter, simple or proliferous-branching near the apex; 

 branches fertile, similar to the primary stems but conspicuously reduced in size; 

 sheaths cylindric, not dilated above, variable, usually with a black band at the 

 base and apex, with the central portion whitish-gray to pinkish, the ridges 

 obscurely keeled, 5-12 mm. long; marginal teeth of the sheaths long and flexuous, 

 reddish-brown to almost black, usually with a narrow whitish hyaline border, 

 subpersistent to deciduous; cones ovoid to cylindric-ellipsoid, apiculate, 1.5-2.5 

 cm. long, 5-10 mm. in diameter. E. prealtum Raf., E. robustum A. Br., E. 

 hyemale var. robustum (A.Br.) A. A. Eat. 



In sandy or loamy soil in open or wooded areas along streams and on alluvial 

 flats, in seepage and on wet ledges, rather generally distributed throughout Okla. 

 and Tex. but most frequent in the Blackland Prairies and on the Edwards Plateau 

 in the latter state, through N.M. to Ariz. (Apache, Navajo and Coconio, s. to 

 Cochise, Santa Cruz and Pima cos.); represented in most of the U.S. and Can. 

 as well as in Mex. and Euras. 



Two insignificant forms of this species occur in Texas; f. Drummondii (Milde) 

 Broun having very tight sheaths adorned with black and white rings, and f. 

 texanum (Milde) Broun with long green ampliated sheaths. 



This is our largest species in the genus Equisetum. It is one of a number of 

 species in the genus that assimilate a large amount of silica. Because of the 

 abundant storage of silica in the stem, they were at one time utilized in rural 

 districts in this country and in the Old World to scour metal kitchen utensils, 

 giving rise to the name "scouring-rush." "\.'-'J'^> 



Fam. 6. Ophioglossaceae Presl. Adder's-Tongue Family 



Succulent or herbaceous terrestrial or occasionally epiphytic plants with short 

 fleshy rhizomes bearing numerous fibrous to tuberous-thickened roots; fronds 

 solitary or clustered, the blade erect or bent in bud (not circinate), erect or 



47 



