A GUIDE AND KEY TO AQUATIC PLANTS 73 



3. Filaments glabrous 4. 



3. Filaments pubescent 2. S. platyphylla. 



4. Inflorescence not branched; leaves not atten- 3. S. subulata. 

 uate. 



4. Inflorescence branched; leaves attenuate 4. S. filtformis. 



5. Leaves without basal lobes 6. 



5. Leaves, at least some of them, with basal lobes 16. 



6. Pedicels of pistillate flowers as long (or nearly 7. 



so) as staminate. 

 6. Pedicels of pistillate flowers very short or 15. 

 nearly wanting. 



7. Filaments not dilated, slender 8. 



7. Filaments dilated, relatively short 10. 



8. Bracts and sepals granular-papillose 5. S. falcata. 



8. Bracts and §epals ribbed. __ 9. 



9. Acbene gradually long-beaked; dorsal wing thick and 6. S. lancifolia. 



even. 

 9. Achene abruptly minutely beaked, dorsal wing thick 7, S. angustifolia. 

 and crested. 



10. Leaf-blades 3-sided, often imperfectly devel- 11. 

 oped. 



10. Leaf-blades flat 12. 



11. Achene 2 mm. long with several facial wings; anthers 8. S. teres. 



longer than filaments. 

 11. Achene 1 mm. long with 3 low facial ribs; anthers 9. S. isoetiformis. 

 shorter than filaments. 



12. Achene oval or broadly elliptic 10. S. cycloptera. 



12. Achene cuneate 13. 



13. Beak large, horizontal, at top of achene body 11. <S. mohrii. 



13. Beak minute, borne below top of achene body 14. 



14. Inflorescence simple; achene with lateral 12. S. graminea. 



wings or ribs. 

 14. Inflorescence compound; achene without 13. S. chapmanii. 

 lateral ribs or wings. 

 15. Fruit head not echinate; achene widely-winged and 14. S. macrocarpa. 



short-beaked. 

 15. Fruit head echinate; achene narrowly-winged and 15. S. rigida. 

 long-beaked. 



16. Achene minutely beaked . 12. S. graminea. 



16. Achene prominently beaked 17. 



17. Beak of achene horizontal or nearly so 16. S. latifolia. 



17. Beak of achene erect 18. 



18. Filaments pubescent 19. 



18. Filaments glabrous. 17. S. longirostr a. 



19. Pistillate pedicels very short; sepals and bracts glab- 15. S. rigida. 



rous. 

 19. Pistillate pedicels elongate; sepals and bracts pubes- 18. S. viscosa. 

 cent, 



1. S. montevidensis C. &. S. Giant Arrow-leaf — Noted by the senior 

 author only in ditches, marshes, and ponds along the coast but 

 probably occurs elsewhere. Is easily distinguished by its gigantic 

 size — the leaves sometimes reach a half a meter in length. 



