192 



CYPEEACEAE 



Style long, its branches much shorter than the united lower part. 

 Spikelets in 1-4 dense globose heads. 



Achene truncate, tipped by a subulate tubercle, ciliate. 1. R. Tracyi. 



Achene obovoid, tipped by a conic tubercle, not ciliate. 2. R. solitaria. 



Spikelets in panicled clusters : achene capped by a stout tubercle. 



Mature spikelets about 1 cm. long : tubercle slightly longer than the achene. 3. R. Indianolensis. 

 Mature spikelets much over 1 cm. long : tubercle several times longer than 



the achene. 4. R. corniculata. 



Style short, its branches as long as the united part or longer. 

 Perianth-bristles none or very short. 



Achene transversely wrinkled. 5. R. pusilla. 



Achene smooth or reticulated. 



Achene reticulated, 0.5-0.7 mm. long : spikelets loosely corymbose. 6. R. divergent. 



Achene smooth, 1.5-2 mm. long : spikelets corymbose-capitate. 



Stem-leaves with blades 0.7 mm. wide or less : spikelets 3-4 mm. long. 7. R. Cfiaimanii. 

 Stem-leaves with blades 1.5-2.5 mm. wide : spikelets 4-6 mm. long. 8. R. pallida. 



Perianth- bristles present and usually well developed. 

 Bristles plumose : achene wrinkled. 



Spikelets solitaiy or 2-4 together, 6-8 mm. long. 9. R. oligantha. 



Spikelets numerous, clustered, 2.5-4 mm. long. 



Perianth-bristles plumose nearly or quite to the top. 



Stems slender, 1.5-3.5 dm. tall : spikelets small. 10. R. plumosa. 



Stems stout, 3-6 dm tall : spikelets large. 11. R. intermedia. 



Perianth-bristles plumose below the middle or only near the base. 12. R. scmiplumosa. 

 Bristles not plumose. 



Bristles retrorsely barbed. 



Scales pale green or white : perianth-bristles 9-24. 13. R. alba. 



Scales brown : perianth-bristles 6. 



Spikelets few to numerous in rather loose, often panicled clusters. 14. R. glomerata. 

 Spikelets numerous, in 2-4 dense globose heads. 



Spikelets 5-6 mm. long : achene 2.5 mm. long. 15. R. axillaris. 



Spikelets 3-3.5 mm. long : achene 1.5 mm. long. 16. R. microcephala. 



Bristles upwardly barbed. 



Achene smooth or cancellate, not transversely wrinkled. 

 Achene smooth. 



Tubercle of the achene ciliate to serrulate. 



Leaf-blades flat. 17. R. fuscoides. 



Leaf-blades channeled, involute, filiform or nearly so. 



Achene linear-oblong : perianth-bristles much overtopping 



the tubercle. 18. R. Curtissii. 



Achene obovoid : perianth-bristles not longer than the 



achene and tubercle, or scarcely so. 



Achene 1 mm. long or less, light brown. 19. R.fllifolia. 



Achene 1.5-2 mm. long, dark brown. 20. R. leptorhyncha. 



Tubercle of the achene smooth or merely granular. 

 Perianth-bristles as long as the achene or longer. 

 Leaf-blades 0.5-2 mm. wide. 



Perianth-bristles about as long as the achene. 21. R. distans. 



Perianth-bristles much longer than the achene. 22. R. gracilenta. 



Leaf-blades 2-7 mm. wide. 23. R. Baldwinii. 



Perianth-bristles much shorter than the achene, sometimes 



very short. 

 Leaf-blades 0.5-3 mm. wide : spikelets 2-5 mm. long. 



Leaf-blades narrowly linear : spikelets 2-3 mm. long. 24. R. fasdndaris. 

 Leaf-blades bristle-like, fi^rm : spikelets 4-5 mm. long. 25. R. brachychaeta. 

 Leaf-blades 4-10 mm. wide : spikelets 6-8 mm. long. 26. R. dodecandra. 



Achene cancellate. 



Leaf-blades broadly linear, blunt or merely acute : achene 1.5 



mm. long. 27. R. ciliata. 



Leaf-blades narrowly linear, attenuate. 



Achenes 2.5 mm. long, equalling or shorter than the bristles. 28. R. Grayi. 

 Achenes 1.5 mm. long, much longer than the bristles. 29. R. Ptankii. 



Achene transversely wrinkled. 



Perianth-bristles shorter than the achene. 



Leaf-blades and stems filiform : spikelets filiform-pedicelled. 30. R. rariflora. 

 Leaf-blades not filiform, flat or involute: spikelets sessile or 



short- pedicelled. 

 Leaf-blades involute. 



Achene flat, 1.5 mm. long, continuous with the tubercle. 31. R. Torreyana. 

 Achene strongly biconvex, 2 mm. long, constricted under 



the tubercle. 32. R. Earlei. 



Leaf-blades flat. 



Achene biconvex, not constricted under the tubercle. 



Achene 1 mm. long : tubercle depressed, wider than high. 33. R. perplexa. 

 Achene 1.5 mm. long : tubercle conic, about as high as "^ 



wide. 34. R. cymoscT. 



Achene compressed, constricted under the tubercle. 35. R. c'ompressa. 



Perianth-bristles as long as the achene or longer. 

 A. Spikelets ovoid to globular, 2-4 mm. long. 

 a. Achene not stipitate. 

 * Tubercle setose. 



f Spikelets 1-3-flowered. 



Perianth-bristles not longer than the achene and 



tubercle. 36. R.patula. 



Perianth-bristles longer than the achene and tubercle. 



Achene broadly or orbicular-obovoid. 37. R. caduca. 



Achene narrowly obovoid. 38. R. mixta. 



