98 GRAMINEAE (GRASS FAMILY) 



tical, about 1-5 mm. long, sparsely pubescent with minutely glandular hairs, 

 (P. fluitans Ell.) In water or mud, Va. to Okla., and south w. 



2. P. dissdctum L. Sheaths glabrous ; blades 1-5 cm. long, 2-4 mm. wide; 

 racemes 3-7 ; spikelets oval, glabrous, 2-2.3 mm. long. (P. membranaceum 

 Walt. ; P. Walterianum Schultes.) Wet places, N. J. to s. 111., and southw. 



* * Racemes with a narrow wingless rhachis ; sheaths compressed. 

 - One raceme terminal, often l-several lateral. 



-* One or more naked raceme-bearing branches from the uppermost sheath; 

 culms tufted, often reclining; racemes slender, often curved; spikelets in 

 pairs, 1.5-2 mm. long, broadly oval or obovate; leaves ciliate on the margin. 



= Spikelets 1.5 mm. long. 



3. P. longipedunculatum Le Conte. Culms reclining, 3-5 dm. long ; leaves 

 mostly near the base, 3-9 cm. long, 4-6 mm. wide, midnerve and margins ciliate ; 

 sheaths pilose at the throat ; racemes 1 or 2, 3-6 cm. long, usually curved, on 

 long slender peduncles ; spikelets glabrous. Sandy soil, Ky. and southw. 



4. P. setaceum Michx. Culms slender, erect or ascending, 4-6 dm. high, 

 smooth ; sheaths hirsute, especially the lower ones ; blades about 1-2 dm. long, 

 2-6 mm. wide (upper reduced), densely pubescent ; racemes slender, usually 

 single, long-peduncled, 5-10 cm. long ; spikelets ovate, finely pubescent and 

 glandular-spotted. Dry sandy fields and pine barrens, N. H. to Neb., Fla., and 

 Tex. Aug.-Oct. 



= Spikelets 2 mm. long. 



a. Spikelets glabrous. 



5. P. ciliatif61ium Michx. Erect, 4-8 dm. high; leaves 0.7-2.5 dm. long, 

 6-15 mm. wide, glabrous; racemes usually single, 5-10 cm. long; spikelets 

 about 2 mm. long, glabrous, green. Sandy soil, Md. to Fla., and Miss. 



6. P. pubescens Muhl. Culms slender, erect, 4-8 dm. high, hirsute below 

 the racemes; sheaths usually glabrous; blades 1-2 dm. long, 3-6 mm. wide, 

 long-pubescent on both surfaces; racemes usually single; spikelets 2 mm. long, 

 glabrous. Fields and dry woods, N. Y. to Del., Miss., and Tex. Aug., Sept. 



7. P. Muhlenb6rgii Nash. Culms more robust than in the preceding, 

 spreading or reclining, glabrous ; sheaths pubescent or nearly glabrous ; blades 

 hardly 2 dm. long, 7-10 mm. wide, long-pubescent on both surfaces ; racemes 

 usually single ; spikelets 2 mm. long, glabrous. Fields and sandy soil, N. H. to 

 Mo., southw. to Fla. and Tex. Aug.-Oct. 



8. P. stramineum Nash. Culms spreading or prostrate, 2-8 dm. long; 

 sheaths ciliate on the margin, otherwise glabrous or the lowest pubescent ; blades 

 about 1 dm. long, crinkly on the ciliate margin, finely pubescent, often with a 

 few scattered long hairs; racemes 1-3 (mostly 2), 4-10 cm. long ; spikelets 

 straw-colored, 2 mm. long, orbicular, smooth. Sandy soil, Neb. to Mo. and 

 southw. July-Sept. 



a a. Spikelets pubescent. 



9. P. Bushii Nash. Culms erect, 8-10 dm. high ; lower sheaths pubescent, the 

 upper pilose on the margin only ; blades 5-20 cm. long, 5-15 mm. wide, softly 

 and densely pubescent on both surfaces; racemes 2 or 3, 10-12 cm. long; 

 spikelets 2-2.2 mm. long, oval, densely pubescent. Dry soil, Neb. to Mo., and 

 Tex. Aug. 



10. P. psamm6philum Nash. Culms prostrate ; similar to P. stramineum 

 but sheaths, both surfaces of the blades, and the oval spikelets softly and densely 

 pubescent; leaves averaging a little longer. (P. pro stratum Nash., not Scribn. 

 & Merr.) Sandy soil, s. N. Y. to Del. Aug., Sept. 



w + No lateral peduncle ; culms stout and often tall. 

 = Spikelets obtuse, glabrous, 

 a. Spikelets singly disposed. 



11. P. laSve Michx. Culms spreading or prostrate, 3-6 dm. long; plant 



