FLORA OF THE DISTRICT OF COLUMBIA. 75 



Spikelets long-pediceled, in an open panicle. 

 Rootstocks present; culms stout and erect; no winter rosette of leaves formed. 

 Spikelets 4-4.5 mm. long (rarely 3.5-5 mm.), beaked; first glume two-thirds 



the length of the spikelet or more "/ ""I.' u'^i Th 



Spikelets not over 3.2 mm. long, not beaked; first glume about half the length 



ofthespikelet 7a. P. virgatum cubense. 



Rootstocks wanting; plants usually forming a winter rosetteof basal leaves.. 

 Vernal phase blooming in the early summer, the culms simple with open 

 terminal panicles; the autumnal phase much branched, the panicles reduced 

 and more or less included in the sheaths. (Subgenus Dichanthelium.) 

 Blades elongate, not over 5 mm. wide, 20 times as long as wide. (Depatj- 

 perata ) (See P. bicknellii and P. acuhatum.) 

 Spikelets about 3.5 mm. long, beaked 14. P. depauperatum. 



Spikelets 2-2.7 mm. long, not beaked. 

 m. *v -i ~ .15. P. lmearifohum. 



Sheaths pilose - * 



„, ., r . , 16. P. wernen. 



Sheaths glabrous 



Blades not elongate, usually not more than 10 times as long as wide. 

 Spikelets glabrous. , 



Spikelets about 1.5 mm. long. Nodes bearded; autumnal phase much 



branched, reclining ; . . . .19. P. microcarpon. 



Spikelets 2 mm. long or more. 



Culms soon prostrate, the autumnal phase vinelike 26. P. lucidum. 



Culms erect, the autumnal phase sometimes reclining but not vinehke. 

 Spikelets about 2.5 mm. long, pointed beyond the fruit. 



25. P. yadkinense. 



Spikelets 2 mm. long, not pointed beyond the fruit. 

 Nodes glabrous; autumnal phase erect, branched like a little tree. 



23. P. dichotomum. 

 Nodes at least the lowest, bearded; autumnal phase top-heavy, 



reclining 24. P. barbulatum. 



Spikelets pubescent (sparsely so in P. scribnerianum) . 

 Spikelets 3 mm . long or more . 



Ligule 3-4 mm. long; blades velvety beneath, firm 43. P. raveneln. 



Ligule obsolete; blades not velvety beneath (except in P. bosm mollej. 

 Nodes bearded ; spikelets 4-4.5 mm. long. 



Blades glabrous or nearly so on both surfaces 50. P. boscn. 



Blades velvety beneath 50a. P. boscii molle. 



Nodes not bearded; spikelets mostly less than 4 mm. long. 

 Blades 1.5-4 cm. wide, cordate-clasping. 



Sheaths glabrous; blades minutely ciliate at base. 



49. P. latifolium. 



Sheaths, at least the lower, tuberculate-hispid ; blades not ciliate 



at base 48. P- clandestinum. 



Blades rarely over 1 cm. wide, not cordate-clasping. 

 Pubescence ascending; spikelets 3.5-4 mm. long. 



42. P. oligosanthes. 



Pubescence spreading; spikelets 3.2-3.3 mm. long 



Spikelets obtuse, 3.2-3.3 mm. long 41. P. scribnerianum. 



Spikelets acute, 3 mm. long 45. P. aculeatum. 



Spikelets less than 3 mm. long (see P. clandestinum) . 



Sheaths retrorsely pilose; plants light green, forming sott mats. 



17. P. xalapense. 



Sheaths not retrorsely pilose; plants erect, spreading or finally prostrate 

 but not forming soft mats A > AA ' 



