BULLETIN 
OF THE 
TORREY BOTANICAL CLUB. 
Vol. XIX.] New York, February 10, 1892. [No. 2. 
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 revision 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. 
