204 



NORTH AMERICAN FLORA 



[Volume 17 



Spikelets about 2 mm. long; leaf -blades mostly hirsute. 

 Spikelets about 1.5 mm. long; leaf -blades glabrous. 



X. Agrostoidia. 



Rhizomes absent; culms strongly compressed with keeled sheaths; 

 spikelets not obliquely disposed. 

 Ligules erose or lacerate, not ciliate ; basal leaves in short tufts, the 

 upper usually nearly equaling the terminal panicle. 

 Fruit not stipitate; spikelets not conspicuously secund. 



Spikelets 1.8—2 mm., in occasional specimens 2.2 mm. long; 



panicle-branches ascending or spreading. 

 Spikelets about 2.5 mm. long; panicle-branches erect or 

 nearly so. 

 Fruit stipitate; spikelets 2.5—2,8 mm. long, conspicuously secund. 

 Ligules ciliate ; basal leaves half as long as the culm or more ; panicle 

 much exceeding the upper leaves. 

 Spikelets not more than 2.7 mm., usually 2.5 mm. long, the first 



glume less than half that length; ligules 2—3 mm. long. 

 Spikelets 3—3.5 mm. long, the first glume two thirds to three fourths 

 that length; ligules less than 1 mm. long. 

 Rhizomes present; culms but little compressed; spikelets set obliquely 

 on their appressed pedicels. 

 Panicles open; spikelets 3.4-3.8 mm. long (shorter in exceptional 



specimens) . 

 Panicles more or less contracted; spikelets not more than 2.8 mm. 

 long. 



XI. Laxa. 



lecond glume gibbous, inflated; spikelets pubescent, 

 lecond glume not gibbous nor inflated; spikelets glabrous. 



Spikelets not expanded at maturity by an enlarged sterile palea, 

 pointed. 

 Leaf -blades more than 15 mm. wide; panicle 10-20 cm. wide; 



spikelets about 1.8 mm. long. 

 Leaf -blades less than 15 mm. wide; panicle mostly less than 10 

 cm. wide. 

 Nodes glabrous; spikelets 2.5 mm. long. 



Nodes densely pubescent; spikelets not more than 1.5 mm. 

 long. 

 Spikelets expanded at maturity by the enlarged sterile palea, usually 

 blunt. 

 Panicle-branches subracemose, the spikelets secund; blades at 

 least 5 mm. wide; enlarged sterile palea not conspicuous. 

 Leaf -blades narrowed toward the base. 

 Leaf -blades cordate or truncate at the base. 



Spikelets 2 mm. long; panicle-branches erect or nearly so. 

 Spikelets not more than 1.6 mm. long, usually less; panicle- 

 branches spreading or ascending. 

 Panicles rarely one -fourth as wide as long; spikelets 

 conspicuously secund and regularly disposed. 

 Culms as much as 2 meters long; panicles 25—30 cm. 



long. 

 Culms not more than 1 meter long; panicles 5—15 cm. 

 long. 

 Panicles one third to half as wide as long ; spikelets not 

 conspicuously secund, somewhat irregularly disposed; 

 leaf -blades cordate-clasping. 

 Panicle -branches not racemose; blades scarcely wider than their 

 sheaths; sterile palea conspicuously enlarged. 

 Spikelets not more than 2.4 mm. long; panicles green or pale. 

 Panicle -branches branchlet-bearing throughout their length 



or nearly so. 

 Panicle-branches spikelet- or branchlet-bearing along the 

 upper half or toward the ends only. 

 Spikelets 3 mm. long, congested; panicles dark-purple. 



XII. Stoi<onii?era. 



Spikelets glabrous, glandless; second glume and sterile lemma boat- 

 shaped. 



Leaf -blades not more than 5 cm., usually 2—3 cm., long; second 

 glume rather blunt and shorter than the sterile lemma. 



Leaf -blades 5-11 cm. long; second glume acute, nearly equaling the 

 sterile lemma. 

 Spikelets hispid and with 2 crateriform glands on the sterile lemma; 

 second glume and sterile lemma not boat-shaped. 



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

 long. 



Spikelets 3.6 mm. long; leaf -blades 4-10 cm. long. 



53. P. stenodoides, 



54. P. stenodes. 



55. P. agrostoides, 



56. P. condensum 



57. P. stipitatum. 



58. P. longifolium, 



59. P. Combsii. 



60. P. anceps. 



61. P. rhizomatum. 



62. P. ineptum. 



64. P. stagnatile. 



63. P. longum. 

 65. P. polygonatum, 



69. P. laxum. 



70. P. Stevensianum. 



66. P. millefiorum. 



67. P. pilosum, 



68. P. boliviense. 



71. P. exiguifiorum 



72. P. Hans. 



73. P. cupreum. 



74. P. stoloniferum. 



75. P.frondescens. 



76. P. pulchellum. 



77. P. biglandulare, 



