A GUIDE AND KET TO AQUATIC PLANTS 



95 



13. 

 13. 



15. 

 15. 



17. 

 17. 



ly. 



19. 



21. 

 21. 



23. 

 23. 



Aclicne eliipsoid-obovate, much longer than wide 4. R. inundala. 



Achene broidly-obovate, slightly longer than wide 5. R. careyana. 



6. Perianth- bristles wanting or very short 7. 



6. Perianth-bristles well-developed 8. 



Achene transversely wrinkled.. 6. R. intermixta. 



Achene smooth 7. R. chopmanii. 



8. Perianth-bristles downwardly barbed 9. 



8. Perianth-bristles upwardly barbed 13. 



Clusters of spikelets loo^e . 10. 



Spikelets ir dense globose heads 11. 



10. Achene 1.5-2 mm. long; panicles rather loose; 8. R. glomerata. 

 if achene is 1.5 mm. long .spikelets 2-3 flow- 

 ered. 

 10. Achene 1.5 mm. long, panicles dense; spikelets 9. R. chalarocephala, 

 with 1 perfect flower. 



Acheiies 2.5 mm. long; spikelets 5-6 n^rn. long 10. R. cephalnntha. 



Achenes about 1.5 mm. long; spikelets .3-3.5 mm. long_ 12. 



12. Heads not truly globose, not tightly com- 9. R. chalarocephala. 

 pacted; basal leaves 1-2 mm. wide, invo- 

 lute. 

 12. Heads very compact and globo.se; basal 11.7?. microcephala. 

 leaves 1.5-3 ram. wide, flat. 

 Achenes smooth or cancellate, not transversely 14. 

 wrinkled. 



Achenes transversely w rinkled 20. 



14, Achenes cancellate 12. R. harveyi. 



14. Achenes smooth 15. 



Tubercle of achene serrulate to ciliate 16. 



T u bercle of achene smoot h or gran ular 18. 



16. Achene 1 mm. long, light bro\vn 13. R. filifolia. 



16. Achene 1.5-2 mm. long, dark brown 17. 



Achenes narrowly obovoid, much less than 1 mm. 14. R. fusca. 

 wide. 



Achene broadly obovoid, about 1 mm. wide. . 15. /?. harperi. 



18. Perianth-bristles much longer than achene. _ 16. R. gracilenla. 

 18. Perianth-bristles much shorter than achene.. 19. 



Leaf-blades linear; spikelets 4-5 mm. long . 17. R. fascicularis. 



Leaf-blades bristle-like, filiform; spikelets 2.5-3 mm. 18. R. wrightiana. 

 long. 



20. Perianth-bristles shorter than the achene 21. 



20. Perianth-bristles as long as achene or longer 26. 



Leaf-blades involute 19. R. torreyana^ 



Leaf-blades flat 22. 



22, Achene biconvex, not constricted under 23. 



tubercle. 

 22. Achene compressed, constricted under 20. R. compressu. 

 tubercle. 



Achene 1 mm. long; tubercle wider than high 24. 



Achene 1.5 mm. long; tubercle about as long as wide 21. R. cymosa. 



24. Achene ellipsoidal, manifestly longer than 22. R. edisoniana. 



broad, finely wTinkled. 

 24. Achene nearly orbicular, about as long as 25. 

 broad, coarsely wrinkled. 



