4(3). Stems and leaves mostly partially emersed; leaves typically more than 5 

 mm. wide, sometimes scarious-margined near the base; fruiting 

 heads usually 2 cm. thick or more; stigma about 1.5 mm. long; 



achene beak (including the stigma) well over 2 mm. long 



3. S. emersum. 



4. Stems and leaves typically submersed or floating; leaves mostly less than 5 



mm. wide, not scarious-margined; fruiting heads usually less than 

 2 cm. thick; stigma scarcely 1 mm. long; achene beak (including 

 stigma) about 2 mm. long 4. 5. angustifolium. 



5(3). Leaves soft and flaccid; inflorescence simple or the branches strict and 

 bearing 1 to 6 staminate heads; bracts mostly spreading; fruiting 

 heads 1.5-2.5 cm. thick; stigma 1-1.5 mm. long; achenes usually 

 somewhat stipitate, the body 3-5 mm. long, not noticeably con- 

 stricted; receptacle scarcely alveolate 5. S. americanum. 



5. Leaves firm and rigid; inflorescense commonly branched, the branches zig-zag 



and bearing 3 or more staminate heads and as many as 2 pistillate 

 heads; bracts ascending; fruiting heads 2.5-3.5 cm. thick; stigma 

 L5-3 mm. long; achenes subsessile, the body 5.5-7 mm. long, 

 usually strongly constricted at middle; receptacle fimbrillate- 

 alveolate 6. S. androcladum. 



1. Sparganium eurycarpum Engelm. Broadfruited bur-reed. Fig. 27. 



Stem stout, erect, branching, 5-18 dm. tall; leaves 5-10 dm. long, 7-17 mm. 

 wide, flat, somewhat keeled below, as long as or slightly shorter than the branched 

 inflorescence; pistillate heads 2 to 6 on the main stem or on branches, sessile or 

 usually peduncled, 2-2.5 cm. in diameter in fruit; staminate heads 8 to 12; anthers 

 1-L5 mm. long, elliptic-clavate; perianth scales long-clawed, expanding into a 

 spatulate apex, irregularly shallowly lobed and hyaline-margined at apex, two 

 thirds to three fourths as long as the fruits; style branches usually 2 but often 1 

 in our area, filiform, about 2 mm. long; achenes sessile, hard and thick at maturity, 

 cuneate-obpyramidal, irregularly and obtusely 3- to 5-angled, 6-10 mm. long 

 and 4-8 mm. wide at apex, the top truncate to depressed or very shallowly 

 rounded, the stout beak 2-3 mm. long. , 



Fresh-water or brackish marshes, meadows, ponds, lakes and streams in Okla. 

 (reported from), N.M. (Lincoln and Otero cos.) and Ariz. (Apache and Navajo 

 COS.), May-Oct.; Nfld. to B. C, s. to Va., Mo., Okla., N.M., Ariz, and Calif. 



2. Sparganium minimum (Hartm.) Fries. Fig. 28. 



Slender submersed or suberect plants, 1-8 dm. long; leaves flat, 2-8 mm. wide, 

 without an evident keel; inflorescence simple, rarely over 6 cm. long; fruiting 

 heads 2 to 4, all sessile or the lowest one short-stalked in axils of bracts, 8-15 mm. 

 in diameter; staminate head solitary; perianth scales elliptic to cuneate-spatulate, 

 one half to two thirds as long as the body of the achene; achene with its ellipsoid 

 to obovoid-fusiform somewhat centrally constricted body about 3 mm. long and 

 with a short stipe scarcely 1 mm. long, the beak 1-1.5 mm. long. 



Submerged in shallow water of mt. lake in n. Ariz. (Coconino Co.), June-Sept.; 

 Lab. to Alas., s. to N.J., Tenn., Ariz, and Calif. 



3. Sparganium emersum Rehm. Fig. 29. 



Stem rather stout but sometimes slender, 3-10 dm. taU; leaves 2-8 dm. long, 

 4-8 (-15) mm. wide, slightly keeled to triangular-keeled especiaUy toward the 

 somewhat expanded scarious-margined base, usually well-overtopping the usually 

 simple inflorescence; pistillate heads 2 to 5, the lowest ones peduncled, the upper 

 ones sessile, at least some of them supra-axillary; staminate heads 3 to 8, con- 

 gested or confluent; anthers 1-1.5 mm. long, elliptic-clavate; perianth scales 

 oblanceolate, arose at broadened apex; stigma linear, about 1.5 mm. long; fruiting 



91 



