Braun and Engelmann's North American Equiseta. 83 



es, and become similar to the sterile ones and persistent through 

 the season, (E. subvernalia, Subvernal Equiseta,) as is the case 

 in E. sylvaticum and E. pratense. 



EQUISETUM, Linn. 



§1. Equiseta speiropora : stomata irregularly dispersed over 

 the whole surface of the grooves. 



* Heterophyadica, : fertile stems different from the sterile ones; the former 

 early and discolored ; the latter later and herbaceous. 



t Amcldbola {Vernal Equiseta) : fertile stems simple, never herbaceous, de- 

 ciduous before the full development of the sterile stems. 



1. E. arvense, Linn. — Sterile stems grooved, smoothish ; 

 sheaths consisting of about eleven 1-carinate leaves ; carinas 

 with a very slight furrow on the back ; the commissural furrows 

 between them slight; carinas of the simple branches compressed, 

 rough ; sheaths consisting of four 1-carinate leaves, with herbace- 

 ous ovate-acuminate subsquarrose teeth. Fertile stems simple ; 

 the sheaths consisting of 2-carinate leaves, which, at first connate 

 up to the apex, finally separate into short teeth. 



The sheaths of the fertile and sterile stems are composed (ac- 

 cording to the size of the specimens) of from 7 to 15, but gener- 

 ally 10 to 13 leaves ; the sheaths of the branches are mostly 4-, 

 seldom 3- or 5-toothed. The summit of the sterile stem is atten- 

 uated, and like one of the branches. — We distinguish the follow- 

 ing varieties. 



(?. nemorosum, A. Braun. Large, 12 to 20 inches high ; the 

 branches with a few branchlets. — E. pratense, Roth and others, 

 not Ehrh. In specimens from Missouri, the sheaths have 12 to 

 15 teeth ; the fertile stems are 12 to 15, and the sterile ones 15 

 to 20 inches high : branches frequently 6 or 7 inches long. 



y. decumbens, Meyer, Chi. Hanov. Sterile stems branching 

 from the base, procumbent. In Missouri, sheaths with 7 to 8 

 teeth : stems 4 to 6 inches high ; the lowest branches with a few 

 branchlets. 



8. serotinum, Meyer, Chi. Hanov. The usually sterile her- 

 baceous stems also with fructification. — E. campestre, Schultz, 

 prodr. fl. Starg. 



Hab. Europe, Northern Asia, North America, from Greenland 

 to the Northern States and Virginia, (Pursh,) to Kentucky, 

 (Short,) Missouri, (Engelmann, Riehl,) the Rocky Mountains, 



