WATER-WEED FAMILY 21 



Faimly 11. ELODEACEAG. Water-weed Family. 

 1. PHILOTRIA Raf. Water-weed. 

 Staminate flowers sessile, breaking oft within the spathe; petals wanting. 



1. P. Planchonii. 

 Staminate flowers on elongating pedicels, carrying them to the water surface; petals 

 present. 2. P. iowensis. 



Family 12. POACEAE. Grass Family. 



Spikelets falling from the pedicels entire, naked or enclosed in bristles or bur-like invo- 

 lucres, l-flowered, or if 2-flowered the lower flower staminate; no upper empty 

 gltimes; rachilla not extending above the upper glume. 

 Spikelets round or somewhat compressed dorsaUy; empty glumes manifest; hilum 

 pimctifonu. 

 Lemma and palet hyaline, thin, much more delicate in texture than the empty 

 glumes. 

 Spikelets in pairs, one sessile and the other pedicellate. 



Tribe 1. Andropogoneae. . 

 Spikelets not in pairs (Alopecurus, Polypogon, Cinna, etc.) 



Tribe 6. Agrostideae. 

 Lemma, at least that of the perfect flower, similar in texture to the empty glumes, 

 or thicker and flrmer, never hyaline and thin. 

 Lemma and palet membranous; the first glume usually larger than the rest. 



Tribe 2. ZOTSIEAE. 

 Lemma and palet chartaceous to coriaceous, very different in color and ap- 

 pearance from the remaining glumes. Tribe 3. Paniceae. 

 Spikelets much compressed laterally; empty glumes none or rudimentary; hilum 

 linear. Tribe 4. Ohtzeae. 

 Spikelets with the empty glumes persistent, the rachilla articulated above them, 1-many- 

 flowered; uoper leumlas frequently empty; rachilla often produced beyond the 

 upper lemma. 

 Spikelets borne in an open or spike-like panicle or raceme, usually upon distinct 

 pedicels. 

 Spikelets l-flowered. 



Empty glumes 4; palet l-nerved. Tribe 5. Phalarideae. 



Empty glumes 2, rarely 1; palet 2-nerved (except in Cinna.) 



Tribe 6. Agrostideae. 

 Spikelets 2-mauy-flowered. 



Lemma usually shorter than the empty glumes; the awn dorsal and usually 



bent. Tribe 7. Aveneae. 



Lemma usually longer than the empty glumes; the awn terminal and straight 

 (rarely dorsal in Bromus) or none. Tribe 9. Festuoeae. 



Spikelets in two rows, sessile or nearly so. 



Spikelets on one side of the continuous axis, forming one-sided spikes. 



Tribe 8. Chloride ae. 

 Spikelets alternately on opposite sides of the axis, which is often articulated. 



Tribe 10. Hordeae. 



Tribe 1. ANDROPOGONEAE. 

 Racemes singly disposed; apex of the rachls-internodes with a translucent cup-shaped 



appendage. 1. Schizachtridm. 



Racemes disposed in pairs or more; apex of the rachis-intemodes not appendaged. 

 Rachis-internodes and pedicels sulcate, the median portion translucent, the margins 



thickened. 2. Amphilophis. 



Rachis-intemodes not sulcate. 



Some or all of the racemes se.ssile. 3. Andhopogon. 



AH of the racemes more or less peduncled. 



Pedicellate spikelets wanting. 4. Sorghastrum. 



Pedicellate spikelets present and usually staminate. 5. HoiCDS. 



Tribe 2. ZOYSIEAE. 

 Only one genus represented. 6. PiiEURAPHis. 



Tribe 3. PANICEAE. 

 Spikelets naked, not involucrate. 

 Empty glumes 2. 



Rachis produced beyond the upper spikelet; spikelets narrow. 



39. Spartina. 

 Rachis not so produced ; spikelets globose or obovoid. 



Spikelets obovoid, turgid. 40. Beckmannia. 



Spikelets plano-convex. 7. Paspalum. 



Empty glumes 3. 



Empty glumes not awned. 



Spikelets in very slender 1-sided racemes, which are usually whorled or ap- 

 proximate. 8. STNTHBRISMA. 

 Spikelets in panicles or panicled racemes. 



Spikelets lanceolate, acuminate, long-hairy. 9. Vallota. 



Spikelets orbicular or lanceolate, if the latter, then glabrous. 



10. Panicum. 

 Empty glumes awned or awn-pointed. 11. Echinochloa. 



Spikelets involucrate. „ 



Involucre of bristles. 12. Chaetochloa. 



Involucre of two spine-bearing valves. 13. Cenchrus. 



