604 



of the staminate flowers deep purplish ; fruit globose, 4-furrowed, 2-3 ram. long. 

 Brackish or fresh pools or slow streams, Nfd. to Alaska, s. to Ct., Great L. 

 region, Kan., N. Mex., Ariz., and s. Cal. (Eurasia.) 



3. M. verticillatum L. Leaves flaccid, 1.5-4 cm. long, the flatfish rhachis 

 someichat broader than the linear-filiform segments; floral leaves or bracts 

 similar but firmer, 6-20 mm. long, uniform or nearly so, all much exceeding the 

 flowers ; stigmas somewhat elongate, recurved ; sepals of the staminate flowers 

 pale green to pinkish ; fruit subglobose, the 4 carpels plump, 2.5-3 mm. long. 

 The typical European plant, rare or local with us ; examined only from w. N. Y. 

 and 111. Represented in America chiefly by 



Var. pectinatum Wallr. Spike appearing naked or nearly so, much as in 

 M. spicatum, all or most of the pectinate bracts shorter than or only slightly ex- 

 ceeding the flowers. Fresh or brackish pools, Gaspe" Co., Que., to Sask. and 

 B. C., s. to n. Me., L. Memphremagog, Que., centr. and w. N. Y., Great L. 

 region, Minn., and Utah. (Eurasia.) 



2. TESSAR6NIA Schindler. Stamens 4 ; petals rather persistent. 



* Carpels 1-2-ridged on the back. 

 - Flowers on emersed spikes, the floral leaves chiefly modified. 



4. M. heterophyllum Michx. Stem stout (the base of the spike 2-5 mm. 

 thick) ; leaves whorled in 4's, 5's, or 6's, the submersed 1.5-5 cm. long, the 

 flattened rhachis slightly broader than the linear-filiform segments ; spikes 1-3 

 dm. long ; floral leaves whorled, crowded, ovate to oblanceolate, entire or den- 

 ticulate, thickish, 4-16 mm. long; fruit 1-1.5 mm. long, about as thick, papil- 

 lose-roughened, the carpels 2-ridged on the back, convex on the sides, their styles 

 prominent. Ponds and slow streams, near the coast, Va. to Fla.; also from 

 w. N. Y. and Ont. to Minn., s. to Mo. and Tex. 



5. M. hippuroides Nutt. Similar, more slender ; floral leaves linear to linear- 

 lanceolate, entire to pectinate ; fruit 2 mm. long, about 1 mm. thick, the smooth- 

 ish carpels flattish on the sides, their styles very short. Apparently local, 

 s. Ont. ; also from Wash, to Cal. 



6. M. scabratum Michx. Slender ; leaves variously arranged, verticillate, 

 subverticillate, or scattered, on the same plant, the submersed with linear-capil- 

 lary segments ; the emersed and the floral leaves linear, pectinate-toothed or cut- 

 serrate; fruit 1-1.5 mm. long, about as broad, the carpels with flat sides and 2 

 tuberculate ridges on the back. (M. pinnatum BSP., at least in part ; possibly 

 Potamogeton pinnatum Walt.) Shallow ponds and muddy shores, e. Mass, to 

 S. C., near the coast ; also from w. Ky. and w. Tenn. to la. and Tex. 



t- -i- Flowers in the axils of unmodified submersed leaves. 



7. M. Farw611ii Morong. Slender, flowering below the surface of the water ; 

 leaves all divided into filiform segments, subverticillate or scattered ; flowers 

 solitary in the middle axils ; fruit 2-2.5 mm. long, somewhat narrower, the flat- 

 sided carpels with prominently tuberculate dorsal ridges. Ponds and slow 

 streams, Gaspe" Co., Que., to n. Mich., s. to s. Me., s. N. H., s. Vt., and centr. 

 N. Y. 



* * Carpels rounded and even on the back ; leaves chiefly scattered, or wanting 



on the flowering stems. 



S. M. h&mile (Raf.) Morong. Stems slender, 5-15 cm. high, erect or decum- 

 bent, rooting in the mud; leaves subopposite or alternate, the lower 4-8 mm. 

 long, pinnately divided; floral leaves similar or linear and serrate or entire; 

 flowers mostly perfect; fruit 0.7 mm. long, the subcylindric carpels smooth or 

 minutely papillose. (M. ambiguum, var. limosum Nutt.) Muddy shores and 

 shallow pools, centr. Me. to Vt., s. to Md.; reported from Ind. and 111. to Tenn. 

 and Mo. Forma NXTAHS (DC.) Fernald. Stems elongate and partly submersed ; 

 foliage leaves crowded, sometimes verticillate, larger, with long capillary divi- 

 sions ; spikes emersed; floral leaves as in the typical form. (M. ambiguum 

 Nutt.) Shallow ponds and slow streams. Forma CAPILL\CEUM (Torr.) Fer- 



