206 



NORTH AMERICAN FLORA 



[Volume 17 



Spikelets about 2.4 mm., rarely only 2.1 mm. long; vernal 



leaf -blades 7—12 cm. long; autumnal blades not falcate. 108. P. arenicoloides. 

 Spikelets not more than 2 mm. long; vernal leaf -blades 4-6 



cm. long; autumnal blades much crowded, falcate. 

 Plants glabrous or nearly so; autumnal culms erect, 

 Spikelets not subsecund ; panicle loose and open. 

 Spikelets subsecund along the suberect panicle-branches. 



103. P. aciculare. 



109. P. ovinum. 



110. P. neuranthum. 



XXVI. BlCKKElyLIANA. 



Spikelets 2.5-2.8 mm. long; leaf-blades not more than 9 mm. wifle. 

 Spikelets 3 mm. long; leaf -blades as much as 12 mm. wide. 



One species. 



XXVII. Nudicauua. 



XXVIII. DlCHOTOMA, 



Nodes, at least the lower ones, bearded. 



Spikelets 1.5—1.6 mm. long, glabrous (occasional individuals with 



pubescent spikelets) . 

 Spikelets 2 mm. or more long. 



Spikelets glabrous, 2 mm. long; autumnal phase top-heavy- 

 reclining. 

 Spikelets pubescent. 



I«eaf -blades all velvety; autumnal phase sparingly branched. 

 Leaf -blades glabrous, or only the lower pubescent or velvety; 

 autumnal phase freely branching. 

 Spikelets 2 mm. long; autumnal phase profusely branching. 

 Fruits slightly exposed at maturity; upper leaf -sheaths 



viscid-spotted; autumnal phase erect or reclining. 

 Fruits covered at maturity; leaf -sheaths not viscid- 

 spotted; autumnal phase decumbent, with flabcllate- 

 fascicled branches; a Mexican species. 

 Spikelets 2.2 mm. or more long; autumnal phase less pro- 

 fusely branching. 

 Leaf -sheaths of lower leaves and all the nodes pubescent. 

 Leaf -sheaths and upper nodes glabrous, 

 odes not bearded. 

 Spikelets pubescent. 



Culms erect, never becoming vine -like. 



Primary leaf -blades spreading ; panicles purplish; fruit exposed 



at summit. 

 Primary leaf -blades erect ; panicles green ; fruit covered (wood 

 forms with spreading blades may be distinguished from P. 

 dichotomum by pubescent spikelets, 2.2 mm. long) 

 Culms soon prostrate, vine-like ; branches divaricate. 



Plants bright-green; culms lax; spikelets not more than 2.1 



mm. long. 

 Plants grayish -green; culms stiff; spikelets 2.5 mm. long. 

 Spikelets glabrous. 



Culms erect, or the autumnal phase top-heavy, never prostrate. 

 Spikelets 2 mm. or more long; panicles open. 

 Leaf -blades spreading; spikelets not turgid. 



Spikelets not more than 2 mm. long, not pointed. 



Autumnal phase erect, branched like a little tree; 

 primary leaf -blades rarely more than 5 mm. wide; 

 second glume shorter than fruit and sterile lemma. 

 Autumnal form top-heavy -reclining ; primary leaf- 

 blades 6-10 mm. wide; second glume equaling 

 fruit and sterile lemma. 

 Spikelets 2.2 mm. or more long, pointed; leaf -sheaths 

 bearing pale glandular spots. 

 Leaf -blades erect, firm; spikelets turgid, strongly nerved; 

 plants grayish olive-green. 

 Spikelets not more than 1.6 mm. long; panicles narrow; 

 plants glaucous bluish-green. 

 Culms soon prostrate. 



Plants bright-green; culms lax; spikelets not more than 2.1 

 mm. long. 



Plants grayish-green; culms stiff; spikelets 2.5 mm. long. 



XXIX. SprUTa. 



Panicle narrow, one fourth to one third as wide as long. 

 Panicle open, two thirds as wide as long, or more. 

 Spikelets 1.5 mm. long. 

 Spikelets 1.3 mm. long or less. 



Culms and leaf -sheaths glabrous. 

 Culms and leaf -sheaths appressed -pubescent. 

 Spikelets 1.2-1.3 mm. long. 

 Spikelets not more than 1 mm. long. 



111. P. Bicknellii. 



112. P. calliphyllum. 



113. P. nudicaule. 



114. P. microcarpon 



122. P. barbulatum 

 117. P. annulum. 



115. P. nitidum. 



116. P. multirameum. 



118. P '. mattamuskeetense, 



119. P. Glutei, 



119. P. Clutei. 



120. P. boreale. 



126. P. lucidum. 



127. P. sphagnicola 



121. P. dichotomum, 



122. P. barbulatum. 



123. P. yadkinense. 



124. P. roanokense. 



125. P. caerulescens. 



126. P. lucidum. 



127. P. sphagnicola. 



128. P. spretum. 



129. P. Lindheimeri. 



131. P. longiligulatum, 



130. P. leucothrix. 



132. P. Wrightianum. 



