FLORA OF THE DISTRICT OF COLUMBIA. 75 



Spikeleta 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-thirda 



the length of the spikelet or more 7. P, virgatum. 



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



of the spikelet 7a. P. virgatum cubense. 



Rootstocks wanting; plants usually forming a winter rosette of 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. (Depau- 



PERATA.) (See P. bicknellii and P. aculeatum.) 



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



Spikelets 2-2.7 mm. long, not beaked. 



Sheaths pilose 15. P. linearifolium. 



Sheaths glabrous 16. P. wemeri. 



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

 Spikelets glabrous. 

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



branched, reclining 19. P. microcarpon. 



Spikelets 2 mm. long or more. 



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



Culms erect, the autumnal phase sometimes reclining but not vinelike, 

 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. barbiilatum. 



Spikelets pubescent (sparsely so in P. scribnerianum) . 

 Spikelets 3 mm. long or more. 



Ligule 3-4 mm. long; blades velve*ty beneath, firm 43. P. ravenelii. 



Ligule obsolete; blades not velvety beneath (except in P. boscii molle). 

 Nodes bearded; spikelets 4^.5 mm. long. 



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



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 46. P. aculeatum. 



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

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



17. P. xalapense. 



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



but not forming soft mats a, aa- 



