Eleocharis Cyperaceae 199 



Perennial, with horizontal rootstocks. 



Culms 0.5-5 mm in diameter (in dried material) at the summit of the upper 

 sheath; basal scales of spikelet usually 2 or 3 below the thinner fertile 

 scales; median scales acute; tubercle broadly ovate, as wide as long. 

 10. E. Smallii. 



Culms 0.5-1.5 mm in diameter at the summit of the upper sheath; basal scales 

 of the spikelet solitary, spathiform, usually completely encircling the 

 base of the spikelet; median scales obtuse; tubercle conical, as long as 

 or longer than wide 11. E. calva. 



Styles 3-cleft. 



Achenes less than 2 mm long; style base not confluent with the apex of the achenes, 

 forming a tubercle. 

 Surface of the achene regularly marked off by longitudinal and transverse lines. 

 Culms not more than 0.5 mm in diameter; achenes obscurely 3-angled; bristles 



equaling or longer than the achene or absent 12. E. acicidaris. 



Culms about 1 mm in diameter ; achenes pyriform ; bristles none 



13. E. Wolfii. 



Surface of the achene smooth or pitted, the pits arranged irregularly or in 

 regular, longitudinal lines. 

 Achenes smooth. 



Achenes tui-binate-lenticular. 

 Bristles longer than the achene. 



Spikelets ovoid-cylindric 8. E. obtusa. 



Spikelets ellipsoid 8a. E. obtusa var. ellipsoidalis. 



Bristles shorter than or equaling the achene 9. E. Engelmannii. 



Achenes triangular; bristles not exceeding the achene or absent. 



Mature achenes nearly black, the body not tapering toward the apex, 

 the angles blunt; 1 mm or more long; tubercle closely capping the 



crown of the achene; bristles absent 14. E. Melanocarpa. 



Mature achenes nearly black, the body not tapering toward the apex, the 

 angles blunt; 1 mm or more long; tubercle closely capping the crown 



of the achene; bristles absent 14. E. melanocarpa. 



Achenes pitted, the pits arranged irregularly or in regular, longitudinal 

 lines. 

 Culms slender, erect; style bases depressed. 



Culms 4-8 angled; scales of spikelets obtuse or merely acute, not con- 

 spicuously whitened at the apex. 

 Achenes Wax Yellow (Ridgway Standard), in age becoming golden 

 yellow to dull orange, averaging 1-1.1 mm long (including the 

 style base); pits of achene usually shallow; culms usually 6-8- 



angled 16. E. elliptica. 



Achenes Olivaceous (Ridgway Standard); pits of achene usually deep 



with some of the cell-projections verrucose; culms 5-angled 



17. E. tenuis var. verrucosa. 



Culms flattened; scales of spikelets (except sometimes in var. atrata) with 

 conspicuously whitened, often bifid, acuminate tips. 



Scales chestnut brown 18. E. compressa. 



Scales conspicuously blackened 18a. E. compressa var. atrata. 



Culms capillary, diffusely spreading; scales obtuse; style base narrow- 

 conic, about twice as long as wide; achenes finely pitted in longitudinal 



lines I.E. intermedia. 



Achenes 2-3 mm long; style base confluent with the apex of the achene, not form- 

 ing a tubercle. 

 Culms 1-2 mm in diameter, (2) 3-10 dm long, flattened, erect, or the sterile 

 ones reclining and often rooting at the tips; beak of achene about a third 



as long as the body 19. E. rostellata. 



Culms less than 1 mm wide, 0.5-3 dm high, scarcely flattened, erect; beak of 

 achene about a fourth as long as the body. . . 20. E. pauciflora var. Fernaldii. 



