NAJADACEAE (PONDWEED FAMILY) 69 



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

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

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



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

 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. (/&'. simplex, var. Nuttallii 

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



Var. andr6cladum (Engelrn.) 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 Mo. 



4. S. diversifblium 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 sessile at least the lower supra-axillary, in fruit 2-2.5 cm. in 

 diameter. (8. simplex Man. ed. 6, in great part.) E. Que. to Ct. and S. Da,k. 



Var. acaule (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. angustif61ium Michx. Slender aquatic; stems 3-12 dm. long; leaves 

 exceedingly 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 northw. 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 mostly 

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

 Nfd. and n. N. E. to Cal., and northw. (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, var. fluctuans Morong, at least in part ; 8. 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 northw. (Eurasia.) 



9. S. hyperbbreum 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. in diameter ; nutlets obovoid, 

 rounded at the summit and tipped with 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 leafy, leaves 

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

 ceous, with 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 fruit 

 indehiscent. 



