A GUIDE AND KEY TO AQUATIC PLANTS 91 



15. E. vivipara Link — Very rarely flowers and so is difficult to 

 identify, forms proliferating mats at the surface of ponds, very likely 

 more common than the records indicate. Coastal Plain in distribu- 

 tion, range extends beyond the limits of our territory, not definitely 

 recorded from Alabama or Mississippi. 



16. E. tuberculosa (Michx.) R. & S. — One of the most frequent of 

 the Coastal Plain Spikerushes, easily identified by the enormous 

 tubercle of its achene. Usually in very shallow water or in moist 

 marginal situations, often in acid soil, range includes all of our Coastal 

 Plain. 



17. E. tortilis (Link) Schultes — Much less common than the pre- 

 ceding, primaiily Coastal Plain but also in the Piedmont over most 

 of our territory. 



18. E. melanocarpa Torr. — Distinctive species, known only from 

 South Georgia and North Florida, perhaps because of a lack of data. 

 It has been observed mostly in acid situations. 



19. E. tricostata Torr. — Coastal Plain, South Georgia and North 

 Florida, also known beyond the limits of our territory. 



20. E. haldioinii (Torr.) Chapm. — Collected frequently only in 

 Florida and South Georgia, single record for North Carolina. Fre- 

 quents mostly pine-barrens, noted proliferating in open, grassy lime- 

 sink ponds. 



21. E. microcarva Torr. — Has been collected from all of our States, 

 common in acid moist places in the Coastal Plain. It has two well- 

 marked varieties which are more wide-ranging than the typical plant. 



5. Scirpus L. 



1. Inflorescence subtended by .a single leaf or none, this 2. 



bract appearing like a continuation of the stem. 



1. Inflorescence subtended by 2 or more bracts, leaf- 8. 

 like. 



2. Spikelets 1 1. S. subterminalis. 



2. Spikelets 2-numerous 3. 



3. Spikelets 2-12, appearing lateral, not in umbel-like 4. 

 clusters. 



3. Spikelets in umbel-like clusters, numerous 6. 



4. Plants annual; scapes not sharply 3-angled 2. S. debilis. 



4. Plants perennial ; scapes sharply 3-angled 5. 



5. Scales of spikelet awned, bract much surpass- 3. S. americanus. 



ing inflorescence; spikelet acute. 



5. Scales of spikelet mucronate; bract only 4. S. olneyi. 



slightly surpassing the inflorescence; spike- 

 lets obtuse. 



6. Stems sharply 3-angled; leaves (also 3- 5. S. etuberculalvs. 



angled) as long as scape. 

 0. Stems round; leaves reduced to mere sheaths. . 7. 



