numerous more apically situated primordia never maturing) ; scales ovate to ovate- 

 oblong, firm to membranous, somewhat striate, with a strong greenish keel-like 

 midrib and brown-stramineous sides; bristles about 7, pallid to pure white, quite 

 variable in length but usually about equaling the tubercle; style 2-branched; 

 achenial body obovate to pyriform, 0.8-0.9 (-1) mm. long, biconvex, shining, 

 microscopically pitted, ripening through shades of chartreuse and olive brown 

 to purplish-brown or even purplish-black; tubercle conic, yellow to greenish-white, 

 acute, 0.1-0.2 mm. long, about 0.1 mm. broad, basally very slightly constricted. 

 E. olivacea Torr., E. ocreata (Nees) Steud. 



Rare in moist soil, on mud and in shallow water, sometimes on floating logs, 

 in e. and s.e. Tex. and Edwards Plateau, probably elsewhere, and Ariz. (Pima 

 Co.), spring-fall; e. N.A. w. to Minn, and Tex.; Ariz, and Calif.; V/.I., Mex., 

 S.A. Easily confused with E. caribaea. 



17. Eleocharis caribaea (Rottb.) Blake. Fig. 196. 



Densely tufted annual (when plants are covered slowly with shifting sand the 

 bases elongating upward somewhat like rhizomes) or perhaps rarely perennial; 

 culms 4-30 cm. long, 0.4-1 mm. thick, terete (or striate and sulcate on drying); 

 sheaths apically oblique, firm; spikelet 3-6 mm. long, ovoid to broadly ovoid, 

 obtuse, of 28 to 50 flowers; scales broadly ovate, 1.5-2 mm. long, firm, when 

 mature stramineous to pallid-buff'y and with inconspicuous midrib, obtuse, even- 

 tually serially deciduous from lowest to highest; bristles about 7, dark-colored, 

 usually about equaling the tubercle; style 2-branched; achenial body (0.7-) 

 0.8-1 mm. long, obovate to pyriform in outline, biconvex, ripening through 

 shades of pale-green to purplish-black, shiny; tubercle conic (depressed or acute), 

 (0.05-) 0.1-0.2 mm. long, pallid-greenish or whitish, slightly constricted basally. 



Locally abundant in moist calcareous soil, wet mud, wet lake shore and 

 streams, in Okla. (Carter, Love and Stephens cos.), in most parts of Tex. (absent 

 from Plains Country and e. Tex.), and Ariz. (Gila and Pima cos.), summer-fall; 

 widespread in warmer parts of the world; in Am. n. to Gulf States, casual 

 elsewhere. 



Has been known incorrectly as E. geniculata (L.) R. & S.; the latter is a species 

 of coarse, tropical perennials not occurring in our region. 



18. Eleocharis atropurpurea (Retz.) J. & C. Presl. Fig. 196. 



Densely tufted annual; culms 3-12 cm. long, 0.2-0.3 mm. thick, arcuate- 

 erect, terete (sulcate or striate on drying); sheaths apically oblique, firm; spikelet 

 narrowly ovoid, 2-4 mm. long, of 40 to 80 flowers; scales ovate to narrowly so, 

 about 1 mm. long, obtuse to abruptly acute, firm-membranous, with a green 

 midrib, brown to purplish laterally; bristles several, usually colorless, translucent, 

 about equaling the achenial body or much-reduced; style 2-branched; achenial 

 body 0.5-0.6 (-0.7) mm. long, obovate to pyriform in outline, biconvex, when 

 mature quite jet black, shiny; tubercle conic, about 0.05 mm. long, whitish, 

 constricted basally. 



Rare and local in moist sandy soil, in mud along streams and marshes in Okla. 

 (Blaine and Alfalfa cos.), e. Tex. (Bastrop Co.), Edwards Plateau (Burnet Co.), 

 Plains Country (Hale Co.) and Rio Grande Plains (Hidalgo Co.), and N. M. 

 (Sandoval Co.), scattered, summer; scattered in warmer parts of both hemis- 

 pheres, in Am. n. to la.. Neb., Colo, and Wash. 



19. Eleocharis parvula (R. «& S.) Link. Fig. 197. 



Tufted annual (?) spreading by short stolons or rhizomes 0.2-0.5 mm. thick, 

 forming mats in mud; culms 2-7 (-12) cm. long, 0.1-0.4 mm. thick, usually 

 sulcate or irregularly flattened; sheaths extremely short and inconspicuous, hyaline, 

 often slightly reddish; spikeiets ovoid to cylindric, 2-9 mm. long, stramineous, 



384 



