17 
(2) Subsection Opisthion Benth. 
Rachis of spikes flat, not dilated. 
(a) Spikes digitate, in terminal pairs, or rarely 3 or 4, 
6. P. conjugatum Berg. (Chapm. FI. 8. States, Suppl., p. 666.) Culms decum- 
bent and branching at base, 1 to 2 feet high, slender, smooth ; leaves flat, thin, 2 to3 
inches long, gradually pointed; sheaths compressed, spikes 2, conjugate, divergent 
(rarely with a third), 24 to 3 inches long ; spikelets in 2 rows, one-half line long, 
roundish ovate, ciliate on the margins, empty glumes very thin, 2-nerved, the middle 
nerve wanting.—Louisiana and Mississippi. 
7. P. notatum Flugge. (Vasey in Bull. Torr. Club, xu. 163. Rhizome creep- 
ing; culm simple, erect or ascending ; leaves lanceolate-acuminate, flat, 4 lines wide, 
lower 6 inches long ; sheaths compressed ; spikes 2, 2 to 3 inches long, in 2 series, ovate, 
smooth, obtusish, empty glumes 3- to 5-nerved.—Introduced on ballast ground, Phila- 
delphia. 
8. P. distichum Linn. (Gray’s Manual, 6th ed., p. 629.) Culms decumbent and root- 
ing, becoming erect, 1 to 14 feet high ; leaves flat, 2 to 5 inches long, smooth; sparsely 
pubescent; spikes 2, rarely 3, 1} to 24 inches long; spikelets in 2 rows, ovate, acutish, 
empty glumes 3-nerved, smooth or sparsely hairy, 1 line long or a little more.—Low 
or sandy grounds, Southern States, westward to California. 
9, P. vaginatum Swartz. (Chapm. FI. 8. States, p. 570.) (P. reimarioides Chapm.) 
Stems widely rooting, the ascending branches varying from short and entirely cov- 
ered with the leaf sheaths to slenderer and 1 foot long, with the leaves distant ; 
leaves rarely flat, mostly involute and almost subulate; the sheaths loose and 
large; spikes 2 to 4, 1 to 2 inches long; spikelets in 2 rows, ovate-lanceolate, acute 
or acuminate, 1} lines long or more, empty glumes 3-nerved.—In ditches and wet 
ground, Florida near the Gulf coast. 
It is difficult to distinguish some forms of this from the preceding species. 
(b) Spikes: single and terminal, or one terminal and one (rarely more) additional, ap- 
proximate, with sometimes axillary peduncled ones. 
10. P. monostachyum Vasey. Chapm. Fl. 8. States, Suppl, p. 665. Culms 
erect, stout, rigid, smooth, 2 to 3 feet, the upper joint very long; lower sheaths in- 
flated, longer than the intern sdes, ligule short, obtuse, blade elongated (the lower 1 
foot or more), convolute, rigid; spike 6 to 8 inches long, erect, the spikelets imbricate, 
about 14 lines long, smooth ; first glume 3-nerved, rather shorter than the spikelet, 
second glume equaling the flowering one; occasionally with a long peduncled ax- 
illary spike, and sometimes the spikelets with a third small sterile glume.—Southern 
Flora (Dr. Garber) and Texas (G. C, Nealley). 
Differs from P. rectum Nees. in its much stouter culm and leaves, and twice as Jong 
a spike. . 
11. P. setaceum Michx. (Gray’s Manual, 6th ed., p. 628.) (P. debile and P. cilia- 
tifolium Michx.) Culms decumbent or erect, 1 to 2 feet high, slender; leaves 2 to 6 
inches long, variable in width, swooth or pubescent; sheaths generally hairy ; spikes 
slender, the terminal one long-peduneled, 2 to 4 inches long; rachis narrow; spike- 
lets in pairs in two rows, shortly pediceled, about three-fourths line, ovate, obtuse, 
smooth, or pubescent.— Widespread, New England to Florida, westward to Texas and 
Mexico. Var. CILIATIFOLIUM (P. ciliatifolium, P. dasyphyllum Ell.) Culms stouter 
and taller, leaves 4 to 6 lines wide, hairy on the margins or all over; spikelets 
larger, smooth or pubescent, and in one form grandular.—Maryland to Florida and 
Texas. 
12974—No. 1——2_ [eb. 25, 1892.] 
