NAJABACEAE QPONDWEED FAMILY) 69 



2-seeded, 7-8 mm. long when mature, with a broad and depressed or refuse sum- 

 mit abrtiptly tipped in the center. — Borders of ponds, lakes, and rivers, N. S. and 

 Me., southw., and westw. to the Pacific, chiefly at low altitude. 



2. S. americanum Nutt. Stoutish, 3-7 dm. high ; leaves thin and snft^ 

 6-12 mm. broad; bracts divaricate or arcuate-ascending; inflorescence strictly 

 simple; pistillate heads all axillary., sessile or nearly so, in fruit 1.8-2.6 cm. in 

 diameter; fruit dull, the beak 2.5-4 mm. long. {S. simplex., var. Nuttallii 

 Engehn.) — Bogs and muddy shores, N. B. to la. and Va. (E. Asia.) 



Var. andr6ciadum (^Engelm.) Fernald & Eames. Inflorescence bearing 

 from its lower axils 1-2 weak branches. (^S. simplex., var. Engelm.) — Similar 

 places, Nfd. to Minn., Mo., and Fla. 



3. S. lucidum Fernald & Eames. Similar, but taller (7.5-9 dm. high) ; 

 leaves firmer, strongly carinate, much overtopping the simple or forking inflo- 

 rescence ; pistillate heads in maturity 3 cm. or more in diameter ; fruit lustrous^ 

 the beak 5-7 mm. long. — Muddy shores, Mass. to Pa. ; also 111. and ]\Io. . 



4. S. diversif51ium Graebner. Erect, stoutish, 3-6 dm. high ; leaves delicate, 

 cellular-reticulated., 4-9 mm. wide, with a broad scarious margin toward the 

 base ; heads chiefly sessde at least the lower supra-axillary., in fruit 2-2.5 cm. in 

 diameter. {S. simplex Man. ed. 6, in great part.) — E. Que. to Ct. and S Dak, 



Var. acaiile (Beeby) Fernald & Eames. Dwarf, 1-3 dm. high ; pistillate 

 heads smaller, 1.5-2 cm. in diameter, mostly crowded. (Var. nanum Graebner.) 



— Nfd. tola, and W. Va. 



5 S angustif51ium Michx. Slender aquatic; stems 3-12 dm. long; leaves 

 e'.K,zeeaingly long and narrow., opaque; inflorescence simple; heads somewhat 

 supra-axillary, the lower ones often peduncled, in fruit 1.3-2 cm. in diameter. 

 — Ponds and slow streams, Nfd. to N. E., westw. and north w. to Ore. and 

 Alaska. 



6. S. simplex Huds. Coarser and in America distinctly aquatic; stems 3-10 

 dm. long; leaves 4-9 mm. broad; inflorescence simple, elongated ; heads mo-.^tly 

 supra-axillary, the lowermost long-peduncled, in fruit 2-2.5 cm. in diameter. — 

 Nfd. and n. N. E. to Cal., and north w. (Eu.) 



7. S. fluctuans (Morong) Robinson. Of medium size for the genus, 0.5-1 m. 

 high ; leaves 7-12 mm. broad ; inflorescence branched ; each of 2 or 3 branches 

 bearing 3-5 heads, usually but 1-3 of the lowermost fertile ; these at maturity 

 2 cm. in diameter ; nutlets with outer coat of firm texture, beaked by a persistent 

 gladiate-falcate style, tipped with a short ovoid or oblong stigma. (S. androcla- 

 dum, vox. fluctuans Morong, at least in part ; S. simplex., var. fluitans Engelm.) 



— Margins of cool lakes, usually at a depth of about 1 m., n. N. B. and adjacent 

 Que. to Pa. and Minn. 



8. S. minimum Fries. Slender, 1-4 dm. high ; leaves grass-like, flat, thin, 

 usually floating, 2-4 mm. broad ; inflorescence simple ; heads mostly sessile, the 

 fertile at length 1 cm. in diameter; the nutlets smooth, conically narrowed to a 

 short but slender straightish beak tipped with a short ovoid or oblong stigma. — 

 Cold shallow water, N. B. to Pa., Mich., Col., Wash., and north w. (Eurasia.) 



9. S. hyperb5reum Laestad. Slender, flexuous, 2-4 dm. high ; leaves 1-4 mm. 

 broad, the cauline somewhat saccate at the base ; inflorescence simple ; the 

 lower heads usually peduncled, in fruit 8-10 mm. m diameter; nutlets obovoid, 

 rounded at the summit and tipped vnth a sessile short-oblong stigma. — Cape 

 Breton (ace. to Macoun) and northw. to Greeul. (N. Eurasia.) 



NAJAdAcEAE (Pondweed Family) 



Marsh or mostly immersed aquatic herbs, with stems jointed and T-eafy., leaves 

 sheathing at base or stipulate, and flowers perfect or unisexual, often spatha- 

 ceous, ivith perianth of 4 or 6 herbaceous distinct valvate segments., or mem- 

 branous and tubular or cup-shaped, or none. Stamens 1, 2, 4, or 6, with 

 extrorse anthers. Ovaries 1-6, distinct, 1-celled, usually 1-ovuled, in irui/ 

 indehiscent. 



