A GUIDE AND KEY TO AQUATIC PLANTS 99 



4. Perigynium abruptly contracted to a beak 5. 



4. Perigynium gradually narrowed to a beak 0. 



5. Perigynium yellowish: opaque part of leaf-sheath 



transver.sely-\v'rinkled . 2. C. vulpinoidea. 



5. Perigynium bro'vnish; opaque part of leaf-sheath nut 



wrinkled - . 3. C. decomposita. 



('). Wing of perigj'nium abruptly narrowed near 



the middle of body A . C . tribuloides . 



6. Wing of perigynium not narrowed near middle 



of body . 7. 



7. Scales of spikelet obtuse or acute; acheues not slenderly 



stipitate - 8. 



7. Scales of spikelet long-accuminate to aristate; achenes 



slenderly stipitate 5. C. alala. 



8. Tips of perigynia appressed 6. C. longii. 



8. Tips of perigynia spreading ._ ._ 7. C albolutescens . 



9. Perigynium 4 to 6 mm. long, without a disk-like base; 

 beak I to 2 times length of body; leaf-sheaths not 



red-dotted within 10. 



0. Perigynium 6 to 7 mm. long, with a hard disk-like 

 base; beak 2-3 times length of body; leaf-sheaths 



red-dotted within . . . S. C. crus-corvi. 



10. Sheaths transversely wrinkled within, easily 



broken, not thickened at mouth. . 9. C. stipata. 



iO. Sheaths not transversely wrinkled within, not 



easily broken, thickened at mouth 10. C. laevi-vaginata. 



11. Lowest bract strongly green-sheathing; beak of peri- 

 gynium bidentate, but with weak teeth il. C cherokeensis. 



1 1 . Lowest bract not strongly green-sheathing, or if so peri- 

 gynium with strongl}' bidentate apex with stiff teelh_ 12. 



12. Perigynium beakless or very short beaked 13. 



12. Perigynium strongly beaked; beak strongly 



bidentate 17. 



]?v. Terminal spike, if staminate, without rough-awned 



scales 14. 



13. Terminal spike staminate; scales rough-awned 15. 



14. Terminal spike staminate; lateral spikes slen- 

 der-stalked, the lower drooping; pistillate 

 scales obtuse or acute, shorter than the 



perigynia_. 12. C. hnrrattii. 



14. Terminal .spike with pistillate .lowers upper- 

 most; lateral spikes short-stalked or sessile, 

 erect; pistillate scales strongly awned, ex- 

 ceeding the perigynia 13. C. buxbuamii. 



lo. Perigynium strongly ribbed; staminate scales gradu- 

 ally awned . 14. C. joorii. 



15. Perigynium nerved; staminate Scales abruptly awned_ 16. 

 16. Pistillate spikes erect; perigynium strongly- 

 nerved 15. C. verrucosa. 



16. Pistillate spikes nodding; perigynium ob- 

 scurely nerved 16. C. glaucescens. 



17. Style jointed with achene 17. C. walteriana. 



17. Style continuous with achene 18. 



