464 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Stems generally evergreen, not dimorphous, usually simple; branches 

 when present, similar to the stem; spikes usually apiculate; stomata 

 in regular rows. Hippochaete. 



Of the genus Equisetimi (Tourn.) L., the type species is E. 

 arvense; of Hippochaete Milde, //. hy emails . I have not been 

 able to verify Milde's authorship of the genus but according to 

 Ascherson and Graebner, ]\Iilde pubHshed it in the Botanische 

 Zeitung for 1865, p. 297. The genus is readily subdivided into 

 two sections. The species with evergreen stems and apiculate 

 spikes form a group that may be known as section Euhippochaete; 

 those with annual stems and generally obtuse spikes may be known 

 as section Ambigua. 



The chief character separating the sections is the duration of 

 the stem; those separating the species are to be found in the 

 ridges and sheaths, whether concave and biangulate, or convex 

 and banded, campanulate or cylindrical. Following out these 

 lines of differentiation, the species will be assembled in a more 

 natural grouping than by any other method. 



Key to the species 



Stems evergreen, spikes apiculate (Euhippochaete). 

 Ridges concave, biangulate. 



Ridges narrowly concave, numerous. 

 Sheaths cylindrical, tight. 



Centrum 3/4 the diameter of the stem, 

 teeth deciduous or more or less 



persistent. H. hyemalis var. californica. 



Centrum, 1/2 the diameter of the stem; 



teeth and awns persistent. H. hyemalis var. Jesupi. 



Centrum 1/3 the diameter of the stem; 



awns deciduous. //. hyemalis var. alaskana. 



Sheaths campanulate, loose. 



Centrum 1/3 the diameter of the stem; 



teeth iKTsistent, awns deciduous. //. variegata. 



Centrum 1/6 the diameter of the stem 



to obsoleteness. //. variegata var. anceps. 



Ridges broadly and deeply concave, these and 



the teeth three. //. scirpoides. 



Ridges rounded, not biangulate. 

 Sheaths cylindrical, tight. 

 Stems simple. 



Sheaths broader than long, teeth per- 

 sistent. //. prcalta. 

 Sheaths longer than broad, teeth cadu- 

 cous. //. prealta var. affinis. 



