200 



NORTH AMERICAN FI/ORA 



[Volume 17 



Vernal culms slender 

 btit not delicate, 

 rarely less than 

 40 cm. high; 

 spikelets 2-2.9 

 mm. long (1.5 

 mm. in P. micro- 

 Car pon and P. 

 caerulescens). 

 l^ower internodes 

 short, upper elon- 

 gate, producing a 



nearly naked 



culm, leafy at 

 base; spikelets 

 narrowly ovate, 

 2.7-2.9 mm. long. 

 Lower internodes 

 not short; vernal 

 culms about even- 

 ly leafy through- 

 out; spikelets el- 

 liptic or obovate, 

 not more than 2.5 

 mm. long. 



Basal leaves similar to culm-leaves, not forming a winter rosette; 

 spikelets all fertile. 

 Fruit transversely rugose (faintly so in P. plenum). 

 Plants annual. 

 Plants perennial. 



Inflorescence consisting of several spike-like racemes 



along a main axis. 

 Inflorescence an open panicle. 

 Fruit not transversely rugose. 



First glume truncate or triangular- tipped, not more than 

 one fourth the length of the narrow, acute or acuminate, 

 glabrous spikelet. 

 First glume not truncate (except in P. rep ens) . 

 Plants annual. 



Spikelets tuberculate. 

 Spikelets not tuberculate. 



Spikelets less than 1.5 mm. long. 

 Spikelets more than 1.5 mm. long. 

 Plants perennial. 



Apex of the fertile lemma laterally compressed into a 



crest; spikelets 5.5-6 mm. long. 

 Apex of the fertile lemma not crested. 



Spikelets short-pediceled along one side of the 

 main branches of the panicle, forming 

 narrow or spike-like racemes, sometimes 

 somewhat aggregated toward the ends of 

 branches (see also IX. Tenera). 

 First glume nearly equaling the sterile 

 lemma. 

 Racemes spreading ; fruit not more than 

 one third the length of the acuminate 

 spikelet. 

 Racemes appressed; fruit nearly as long 

 as the blunt spikelet. 

 First glume much shorter than the sterile 

 lemma. 

 Leaf -blades ovate to lanceolate, with 

 short petioles; plants creeping and 

 rooting at the nodes, the flower-culms 

 sometimes upright. 

 Leaf -blades linear or elongate-lanceolate, 

 not petioled. 

 Panicle long (15-30 cm.) and very 

 narrow, the branches erect or 

 nearly so; fruit rather thin and 

 soft, the palea scarcely enclosed. 

 Panicle usually open (at least not 

 long and narrow), the main 

 branches spreading; fruit in- 

 durated, the palea enclosed. 

 Plants erect, rather robust; pan- 

 icle-branches not forming dis- 

 tinct racemes, nor naked below 

 with the spikelets aggregated 



XXVII. Nudicauua, 



XXVIII. DlCHOTOMA. 



III. Fascictji^ata, 



II. Geminata. 

 VII. Maxima. 



IV. DlCHOTOMIFEORA 



XIV. Verrucosa. 



XV. Trichoidia. 

 V. Capii^aria 



XLV. ZlZANIODJlA. 



XLVI. Gymnocarpa, 

 XU. Obtusa. 



XII. Stoujnifera. 



XLIII. Hemitoma. 



