IOWA PTERIDOPHYTA. 155 



sented: Emmet (E. I. Crafty, June, 1884, fruiting); 

 Winnebago (July, 1899, old fruit, branching) ; Hancock 

 (July, 1896, sterile, somewhat branched) ; Hamilton 

 (May, 1882, fertile). 



Equisetum robustum A. Braun, Engelm., Am. Jour. 

 Sci., vol. XVI, p. 88 (1844). 



This species is not rare in the state, but is often con- 

 fused with E. hycmalc and sometimes with E. Itzvigatum. 

 It is readily distinguished from these species, even when 

 sterile, by the short sheaths whose ridges are /rz'-carinate, 

 at least toward their tips. The ridges are four-carinate in 

 the former and two-carinate in the latter. The species 

 grows commonly on wet banks. The following counties 

 are represented: Henry {J. H. Mills, no date) ; Johnson 

 (Mch., and Apr., 1901) ; Linn (May, 1892, fertile ; Jackson 

 (T. H.Macbride, Aug., 1883) ; Winnebago (Sep., 1895) ; 

 Shelby (T. J. Fitzpatrick, May, 1884). The last speci- 

 men is well-fruited. It was labelled E. Icsvigatum, but, 

 though the sheaths are rather elongated, it seems clearly 

 to be the present species. 



Equisetum hyemaee L. 



This species does not seem to be common in the state. 

 Two counties only are represented: Lee (July, 1895); 

 and Des Moines {P. Bartsch, Aug., 1895). It is readily 

 recognized by the slender stems (usually tufted) and by 

 the four-carinate ridges on the elongated sheaths. 



Equisetum l^vigatum A. Braun; Engelm. Am. Jour. 

 Sci. vol. 46, p. 87. (1844). 

 This is the most common species of the genus in the 

 State. It is found most commonly on sandy banks or ridges, 

 often in rather dry places, and does not often produce 

 sterile branches. Some specimens are quite strongly 

 tuberculate, as for example the Lee county specimens 

 (1895) and those from Winnebago and Webster counties. 

 The latter have rather strong transverse tubercles as in E. 



