5(4). Achenial body smooth under low magnification or faintly cellular-reticulate 



under high magnification, the 2 faces strongly convex 



4. R. divergens. 



5. Achenial body with transverse ridges, the 2 faces only sHghtly convex 



5. /?. piisilla. 



6(4). Bristles conspicuously retrorsely barbed (7) 



6. Bristles antrorsely barbed or plumose or absent or smooth (10) 



7(6). Bristles 10 to 20 per achene; spikelets with only 1 fertile flower and this 

 appearing terminal (no rudimentary flower above it); inflorescence 

 usually merely a dense terminal fascicle 9. R. macra. 



7. Bristles fewer; spikelets usually with 2 fertile flowers or one fertile flower and 



a reduced one above it; each culm with several fascicles, one 

 terminal and several axillary, or if only one fascicle then culm 

 capillary (8) 



8(7). Culms capillary; achenes inconspicuously margined, finely granulate to 

 slightly rugulose, achene body 1.7-2.6 mm. long, less than half 

 as wide as long 6. R. capillacea. 



8. Culms 1-3.5 mm. thick basally; achenes with conspicuous pale vdre-like 



margins, smooth, castaneous, usually lustrous, achene body 1.3-1.7 

 mm. long, one half to three fourths as wide as long (9) 



9(8). Central portions of the 2 sides of the achenial body abruptly raised in a 

 hump and polished-buff'y, contrasting with the dark chestnut-brown 

 submarginal flat portions, the margins themselves pale and wirelike; 



leaves basally 5-6 mm. broad; culms basally 2-3.5 mm. thick 



7. R. glomerata. 



9. The 2 sides of the achenial body rather evenly convex all over, grading from 



buffy centrally to darker brownish marginally, the margins them- 

 selves slightly paler and wirelike; leaves basally 2-3 mm. broad; 

 culms basally 1-2 mm. thick 8. R. capitellata. 



10(6). Bristles heavily plumose basally (11) 



10. Bristles antrorsely serrulate or barbed, smooth or these absent (12) 



11(10). .Spikelets 4-7 mm. long, 1 to 5 present per culm, remote on slender 



pedicels; achene 2.3-2.6 mm. long (excluding tubercle) 



10. R. oUganthra. 



1 1 . Spikelets 3-4 mm. long, more numerous, congested in spikelike fascicles; 



achene 1.4-1.8 mm. long (excluding tubercle) 11. R. plumosa. 



12(10). Achenial body smooth (13) 



12. Achenial body with traverse wrinkles or traverse rows of cells with 



sculptured walls (15) 



13(12). Achenial body 0.9-1 mm. long; tubercle 0.4-0.6 mm. long 



12. R. fiUfolia. 



13. Achenial body 1 .3-1 .8 mm. long; tubercle 0.4-2 mm. long (14) 



14(13). Tubercle 0.4-0.7 mm. long 13. R. fascicularis. 



14. Tubercle 1-2 mm. long 14. R. gracilenta. 



15(12). Terminal part of inflorescence of each culm very lax, with only 6 to 12 

 (to 20) spikelets each on a capillary pedicel 3-12 mm. long; culms 

 only 0.6-1 mm. thick 17. R. rariflora. 



15. Terminal fascicle denser with more spikelets or if as few as 12 then either 



denser or else the culm thicker than 1 mm. basally (16) 



470 



