A genus of 150 to 200 species, chiefly in the North Temperate Zone. 



1. Longest glume shorter than 2 mm. (2) 



1. Longest glume longer than 2 mm. (3) 



2(1). Panicle very dense with short scabrous branchlets that are many-flowered 

 nearly to the base; stolons present 1. A. semiverticillata. 



2. Panicle very diffuse; branchlets long and naked most of their length, the spike- 



lets crowded toward the tips; stolons absent 2. A. hyemalis. 



3(1). Tufted perennials without rhizomes or stolons; panicles open and/or 

 diffuse, the branches mostly naked (4) 



3. Perennials with stolons or rhizomes or the lower intemodes reclining and sub- 



rhizomatous; panicles sometimes open but not diffuse, the branches 

 bearing flowers for at least half their length (6) 



4(3). Panicle very diffuse, irregularly rounded, the main branches forking toward 

 the end or above the middle, the pedicels short, the spikelets 

 crowded near the end of the branches 3. A. scabra. 



4. Panicle open but not diffuse, subpyramidal, the main branches forking at or 



below the middle; pedicels and spikelets not as above (5) 



5(4). Spikelets about 2 mm. long; plants of high altitudes, delicate, mostly 1-3 

 dm. tall 4. A. idahoensis. 



5. Spikelets 2-3 mm. long; plants somewhat robust, of lower elevations 



5. A. perennans. 



6(3). Panicles more than 25 mm. broad, the branches spreading; rhizomes pre- 

 sent, 2-3 mm. thick 6. A. stolonifera. 



6. Panicles less than 25 mm. broad, the branches ascending or appressed; 



rhizomes absent but stolons often present (7) 



7(6). Palea present 7. A. palustris. 



7. Palea absent 8. A. exarata. 



1. Agrostis semiverticillata (Forsk.) Christ. Water bentgrass. Fig. 106. 



Stoloniferous perennial freely rooting at the nodes; aerial culms 2-5 dm. long, 

 1-2 mm. thick, leafy; ligule a thin scale 2-7 mm. long; blades 4-14 cm. long, 2-7 

 mm. broad, flat; panicle 3-10 cm. long, 1-3 cm. thick, ellipsoidal, very dense; 

 swollen zone of abscission present on the scabrous pedicellary branchlets below 

 the spikelets; glumes 1.3-2 mm. long, scabrous; lemma about 1 mm. long or 

 shorter, truncate; palea narrow, as long as lemma. Polypogon semiverticillatiis 

 (Forsk.) Hylander. 



At the edges of streams in calcareous mud, along irrigation ditches, seepage 

 and in shallow water, in Okla. (Cimarron Co.), n.-cen. Tex., Edwards Plateau, 

 Plains Country and Trans-Pecos, locally abundant, N.M. (Guadalupe. De Baca 

 and Eddy cos.) and Ariz. (Apache to Mohave, s. to Cochise, Santa Cruz and 

 Pima COS.), Apr. -June and continuing now and then into Nov.; warmer parts of 

 the world, in N. A. n. to Wash., Nev., Ut., Colo., and Tex., introd. from the Old 

 World. 



2. Agrostis hyemalis (Walt.) B.S.P. Spring bentgrass. Fig. 107. 



Tufted perennial; culms 1-6 dm. long, 0.5-1 mm. thick, leafy, erect or the 

 lowermost internodes reclining; ligule a thin scale 1-4 mm. long; blades 3-9 cm. 

 long, 1-2 mm. broad, flat; panicle 5-30 cm. long, at least half as broad at 

 maturity, open and very diffuse, the long branches capillary and mostly naked, 

 branched in the outer third; spikelets crowded at the ends of the branchlets, 

 appressed; glumes 1.5-2.1 mm. long, subequal; lemma 1-1.3 (-1.5) mm. long, 

 awnless; palea absent. 



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