NAJADACEAE (POND WEED FAMILY) 77 



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

 pound, bi-glaiidular 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. — Gasp6 Co., Que., to Hudson 

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



30. P. folibsus Raf. Stem filiform, flattish and very branching ; leaves 

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

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

 peduncles ; fruit roundish-lenticular, the hack 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. niagarfinsis (Tueke'rm.) 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 Reiohenb. 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; ja^ciuncle solitary, very long (0.5-2 dm.), 

 rather thickened upward ; spilce i-i-fiuwered, in fruit continuous, cylindrical; 

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

 epicarp thick and hard ; embryo nearly annular. (P. Tuckermani Hohh'ms.') — 

 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 ; eraersed spikes 0.5-1.5 cm. long ; 

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

 1 mm. long, about 8-toothed on the margin, the lateral keels smooth ; embryo 

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

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

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

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



33. P. dim6rphU3 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. filiffirmis 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 n^ion 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 Rooky Mts. July-Sept. (Eurasia, Afr., Austr.) 



35. P. intSrior 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 occidentalii 

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

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



