THE FERX BULLETIN 



17 



218. Marsilia vestita Hook and Grev. Horse 



Clover. Common : in moist places. Dakota, 

 and Washington to Texas and California ; also 

 in Mexico. 



219. Marsilia vestita tenuifolia (Engelm.) Very 



rare: in moist places. Texas. Only twice col- 

 lected. — M tenuifolia Engelm. 



Pilularia L. 



:220. Pilularia Americana A Br. Pillwort : Water 

 Pepper. Rare; in moist places. Oregon, Cali- 

 fornia and Arkansas; also reported from Chili. 



EQUISETACEAE. 

 Equisetum L. 



221. Equisetum arvense L. Field Horsetail. Very 



abundant : in swamps, woodlands, fields and 

 roadsides. Throughout North America, also in 

 the north temperate and Arctic zones of the 

 Old World. 



This is a most variable species with many 

 named forms of no stability. The following are 

 most important : alpestre, arcticum, boreale, 

 campestre, decumbens, diffusum, irriguum, 

 nanum nemorosum, polystachyon, and pseu- 

 dosylvaticum. All are described in Fern Bul- 

 letin, vols. VII and VIII. 



222. Equisetum Ferrissi Clute. Rare ; in moist 



shades. Northeastern Illinois. 



223. Equisetum fluviatile L. Water Horsetail. 



Common : in shallow ponds and ditches. Vir- 

 ginia, Kansas and Washington to the far 



