NAJADACEAE (PONDWEED FAMILY) 77 



sharp-acuminate, soon revolute, 3-5-nerved, the prominent midrib often com- 

 pound, bi-glandular at base ; stipules 1-2 cm. long, acuminate, scarious and 

 strongly nerved, persistent; peduncles 1.3-3.5 cm. long; spikes elongate, 6-8- 

 flowered ; fruit narrowly oblique-obovoid, about 2 mm. long, the erect style 

 nearly in line with the straightish ventral face. Gaspe* Co., Que., to Hudson 

 Bay, s. to Me., Vt., Mich., and Minn., local. (Eu.) 



30. P. folibsus Raf. Stem Jilt form, Jlattish and very branching ; leaves 

 narrowly linear (2-6 cm. long, 0.3-1 mm. wide), acute, obscurely %-nerved ; 

 stipules obtuse; spikes capitate, l-4(usually 2)-flowered, on short club-shaped 

 peduncles ; fruit roundish-lenticular, the back more or less crested; upper por- 

 tion of the embryo incurved in a circle. (P. pauciflorus Pursh.) Still waters, 

 N.B. to B. C., and south w. July-Sept. 



Var. niagarensis (Tuckerm.) Morong. Stem often longer; leaves larger 

 (4-9 cm. long, 1-2.4 mm. wide), 3-5-nerved at base, very acute and mucronate, 

 narrowed to the subpetiolate base. Running water, Me. to Ont., and southw.; 

 also in Cal. 



31. P. confervoides Reichenb. Very slender and delicate from a creeping 

 rootstock, of a fine light green ; stem filiform with several short and repeatedly 

 dichotomous leaf-bearing branches ; leaves flaccid, thin and flat, but setaceous 

 and tapering nearly to the fineness of a hair (2.5-6.5 cm. long, 0.1-0.5 mm. 

 wide), obscurely 1-3-nerved, with a few coarse reticulations; stipules rather 

 persistent below, 5 mm. long, obtuse ; peduncle solitary, very long (0.5-2 dm.), 

 rather thickened upward ; spike 4-S-flowered, in fruit continuous, cylindrical; 

 fruit thick-lenticular, obscurely S'-keeled ; seed slightly impressed on the sides; 

 epicarp thick and hard; embryo nearly annular. (P. Tuckermani Robbins.) 

 Cold ponds, local, Me. to N. Y., N. J., and Pa. June-Aug. 



32. P. hybridus Michx. Floating leaves (when present) oval to lance-oblong 

 (the largest 2.6 cm. long, 1.2 cm. wide), often acute, longer than the filiform 

 petioles, with about 5-7 nerves beneath deeply impressed ; submersed " leaves 

 very numerous, almost setaceous (2-7 cm. long, 0.1-0.5 mm. wide) ; stipules 

 obtuse, adnate to the base of the lower leaves ; emersed spikes 0.5-1.5 cm. long ; 

 submersed spikes 1-4-flowered, their peduncles frequently recurved; fruit about 

 1 mm. long, about %-toothed on the margin, the lateral keels smooth ; embryo 

 coiled \\ turns. (P. diversifolius Raf.) Shallow quiet waters, Me. to Fla. ; 

 also Mich, to Mont, and Tex. July-Sept. (Mex., W. I.) Var. MULTI-DENTICU- 

 lAxus (Morong) Asch. & Graebn. Fruit 12-toothed on the margin, the lateral 

 keels 6-8-toothed. Ct. to Fla. and La. 



33. P. dim6rphus Raf. Coarser ; blades of the floating leaves with rather 

 dilated petioles, with 5-many nerves beneath deeply impressed ; upper submersed 

 leaves either with or without a lance-oblong or broad-linear proper blade ; the 

 numerous lower ones narrow-linear, tapering toward the. obtuse apex (2-4 cm. 

 long, about 1 mm. wide); stipules early lacerate ; submersed flowers 1-4, on very 

 short erect peduncles; fruit with the back either winged and with 4-5 distinct 

 teeth or wingless and entire ; embryo coiled If turns. (P. Spirillus Tuckerm.) 



-N. B. to Ont., s. to Va., W. Va., and Mo. June-Sept. 



34. P. filif6rmis Pers. Stems from elongate tuberiferous rootstocks, filiform, 

 branching at base, low and very leafy ; leaves pale, filiform, less than 0.5 mm. 

 wide; peduncles much elongated and overtopping the leaves (in one form 

 shorter); spikes of 2-5 whorls, the lowest whorls 0.6-1.5 cm. apart; fruit 

 2.5-3 mm. long, globose-obovoid, not keeled upon the rounded back, tipped with 

 the broad sessile stigma; embryo annular. (P. marinus auth., not L. ?) 

 Shallow water in calcareous regions, e. Que. to Alb., s. to n. Me., n. Vt., w. 

 N. Y., Mich., and the Rocky Mts. July-Sept. (Eurasia, Afr., Austr.) 



35. P. intdrior Rydb. Coarser ; the comparatively stout stems flattened, 

 freely branching above, elongate ; leaves dark green, narrowly linear, 0.5-2 mm. 

 wide ; peduncles of various lengths ; spikes of 4-9 whorls, the upper whorls 

 crowded, the lowest 4-9 mm. apart ; fruit compressed, narrowly oblique-obovoid. 

 the ventral face straightish. (P. filiformis, vars. Macounii and occidentalis 

 Morong.) Mostly in brackish water, P. E. I.; Huds. B. to Assina. and 

 Athabasca, s. to Neb., Col., and Nev. July-Sept. 



