164 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



4. Culms septate, i. e. with bars extending across the culm, these sometimes very- 

 obscure; upper sheaths horizontal at summit, with a conspicuous rigid 

 mucro; achenes pitted-reticulate; spikelets 1 to 2 cm. long, commonly 



pale brown, with numerous rigid acute scales 3. E. nodulosa. 



4. Culms not septate; upper sheaths usually oblique, rarely mucronate; 

 achenes smooth (5) . 

 5. Empty basal scales of the spikelet normally 2 or 3; culms soft, com- 

 pressed; spikelets narrow-cylindric or lanceolate, 1 to 3 cm. long; 



scales pale to dark brown 4. E. macrostachta. 



5. Empty basal scale solitary, encircling the base of the spikelet. 



5. E. CALVA. 



1. Achenes trigonous to nearly terete; styles trifid (6). 



6. Style base confluent with the apex of the achene; achene trigonous, green 



to olivaceous, obovoid to elongate, reticulate or slightly verrucose under 



high magnification, not with longitudinal ribs and cross bars (7). 



7. Culms capillary, 2 to 5 (rarely 7) cm. long, few-flowered; achenes 1 to 1.5 



mm. long, without bristles; minute tubers frequently present among 



the roots: var. anachaeta 6. E. parvula. 



7. Culms 1 mm. (or more) wide, at least 20 cm. long; achenes 2 to 3 mm. 

 long (8). 

 8. Achenes elongate, strongly reticulate; spikelets not proliferous; tubers 



frequently present: var. suksdorfiana 7. E. pauciflora. 



8. Achenes obovoid, with a smooth (almost greasy) surface; spikelets fre- 

 quently proliferous; tubers none 8. E. rostellata. 



6. Style base not confluent with the apex of the achene, usually constricted at 



base (9). 



9. Achenes not cross-ribbed, trigonous, dark brown when mature; plants 



perennial, with creeping rootstocks (10). 



10. Spikelets linear to narrowly-lanceolate, acuminate; scales acute, 



appressed, dark brown (frequently mottled with white) ; achene 



smooth under magnification 9. E. parishii. 



10. Spikelets ovoid to oblong, usually obtuse; scales very obtuse, dull 



brown; achene pitted-reticulate under magnification. 



10. E. MONTEVIDENSIS. 



9. Achenes cross-ribbed between the longitudinal ribs, terete to obscurely 

 trigonous; plants with capillary culms, annual, or perennial with 

 filiform rootstocks; lowest scale fertile (11). 



11. Anthers 0.8 to 1.2 mm. long; scales with a greenish center and reddish 



brown sides; bristles none; plant perennial: var. occidental} s. 



11. E. ACICULARIS. 

 11. Anthers less than 0.5 mm. long (12). 



12. Plant perennial, with light-green spongy culms and filiform creeping 

 rootstocks; bristles exceeding the achenes, rarely lacking. 



14. E. RADICANS. 

 12. Plant annual, forming tufts (i. e. cespitose) ; anthers 0.2 to 0.5 mm. 

 long (13). 

 13. Achenes elliptic to fusiform; cross bars about 30 in a longitudinal 



series 12. E. bella. 



13. Achenes ovoid; cross bars about 15 in a longitudinal series. 



13. E. CANCELLATA. 



1. Eleocharis engelmanni Steud., Syn. PI. Glum. 2: 79. 1855. 

 Flagstaff, Coconino County (Jones 4058), White Mountains, Apache 



County (Griffiths 5271). Maine to Arizona and California. 



Represented in Arizona by var. monticola (Fernald) Svenson, char- 

 acterized chiefly by pale spikelets. 



2. Eleocharis geniculata (L.) Roem. and Schult., Syst. Veg. 2: 150. 



1817. 

 Scirpus genicuiatus L., Sp. PI. 1: 48. 1753. Not of recent 



authors. 

 Eleocharis caribaea (Rottb.) Blake, Rhodora 20: 24. 1918. 



Rye Creek near the Mazatzal Mountains, Gila County (Harrison 

 and Kearney 8369) . Throughout the world, in tropical and subtropical 

 regions. 





