Review of the North American Species of the Genus Xyris. 



By Heinrich Ries. 

 Plate CXXIV. 



While engaged in a study of this genus during the past win- 

 ter, I found great confusion existing among the various species. 

 The most complete list of the North American species thus far 

 published is in Chapman's Flora of the Southern States ; but 

 even here the descriptions are hardly sufficiently accurate, and 

 all the species cannot be maintained. It has therefore seemed 

 to me desirable to present this revjsion of the genus, the arrange- 

 ment of which is based on specimens in the herbarium at Harvard 

 College, Agricultural Department at Washington, and those of 

 Messrs. J. D. Smith, W. M. Canby, as well as the herbarium of 

 Columbia College. The majority of the species are confined to 

 the Southern States. The genus may be defined as follows : 



Perennial, stemless herbs. Roots usually fibrous, sometimes 

 bulbous. Leaves linear or linear-lanceolate, collected about the 

 base of the naked scape. Scales convex, horny, thicker in the 

 middle. Flowers single in the axils of the scales, which are col- 

 lected into a more or less dense spike. Sepals three, the two 

 lateral ones glumaceous and keeled, enclosing a third membran- 

 ous one. Petals three, clawed. Stamens six, three of which are 

 fertile and situated on the claws of the petals, the alternate ones 

 being sterile. Anthers linear. Ovary one-celled, three- valved; 

 the valves bearing the placenta along the middle. Stigma one, 

 style three- cleft. The modifications of the keel of the lateral 

 sepals form valuable specific characters. 



