NAJADACEAE (POND WEED 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 1.3-0.5 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. — Gasp6 Co., Que., to Hudson 

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



80. P. folidsus Haf. Stem filiform, fi,attish and very branching ; leaves 

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

 stipules obtuse; spikes capitate, l-i{2(sually 2)-fl,owered, on shoit 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 die subpetiolate base. — Running water, Me. to Ont., and southw.; 

 also io 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 fl,accid, 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 'i-S-flowered, in fruit continuous, cylindrical ; 

 fruit thick-lenticular, obscurely 3-keeled ; seed slightly impressed on the sides ; 

 epicarp thick ancf hard; embryo nearly annular. (P. Tuckermani Bobbins.) — 

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



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 ?ihom 

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

 coiled 1^ turns. (F. diversifolius Raf.) — Shallow quiet waters, Me. to Fla. ; 

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

 LATDS (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, witli 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 loith 4-5 distinct 

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

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



34. P. filif6rmis Fers. Stems fjom elongate tuberiferous rootstocks, flliform, 

 branching at base, lovj and very leafy ; leaves pcde, 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. Yt., w. 

 N. Y., Mich., and the Rocky Mts. Jtdy-Sept. (Etirasia, Afr., Austr.) 



35. P. interior Rydb. Coarser; the comparatively stout strms flattened, 

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

 wide ; peduncles of various lengths ; spikes of 4-0 whorls, the upper whorls 

 crowded, tht' lowest 4-0 mm. apart ; fruit compresspd. narrowly oblique-obovoid. 

 the ventral face straightish. (P. flliformis. vars. Macouriii and occidoitali." 

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

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



