NAJADACEAE (PONDWEED FAMILY) 75 



8-4 cm. long; spikes 2-2.5 cm. Jong; fruit similar. Ponds and slow streams, 

 local, N. E. to the Great Lakes. Sept., Oct. (Eu.) 



Iti. P. bupleuroides Fernald. Very slender, branching ; leaves orbicular to 



! <ite, <>!>t<(*e,flat, not crisped, drying blackish green or bronze, !-;!." 1-111. 



loiii,'. 1 -\~-nerved; stipules rarely developed, appressed and inconspicuous; 



"lea slender, scarcely spongy, 2-6 ctn. long; spikes 0.7-2 cm. lung ; fruit 



narrowly obovoid, 2.5-3.2 mm. long, the sides flat and deeply pitted, the back 



rounded, slisihtly 3-keeled ; style slender and prominent ; the olive or brownish 



epicarji closely inri'stiny the seed. (P. prrfol tutus Man. ed. 6, in part, not 



L.) Brackish, occasionally fresh, ponds and quiet streams, Nfd. and e. Que. 



to Fla., rarely inland to w. N. Y. and Mich. July-Sept. 



x P. KITEXS Weber and plants closely simulating it in America are infertile 

 and appear to be hybrids of no. 10 with no. 14, 15, or 16. 



17. P. mysticus Morong. Stem very slender and irregularly branching, 

 nearly filiform; leaves oblong-linear (1.5-4 cm. long, 4-6 mm. wide). 5-7- 

 nerved, finely undulate and entire, obtuse or bluntly pointed, abruptly nar- 

 rowing at base, sessile or partly clasping ; spikes few, capitate (4-6-tlowered), 

 on erect peduncles ; fruit (immature) obovoid, small (less than 2 mm. long), 

 obscurely 3-keelrd on the back, a little beaked by the slender recurved style. 

 Locally in brackish ponds, Mass, and Md. Infertile, and probably a hybrid of 

 nos. 16 and 25. 



18. P. CRfspus L. Stem compressed; leaves linear-oblong, sessile or half- 

 clasping, obtuse, serrulate, crisped-wavy, 3-o-nerved; fruit long-beaked; upper 

 portion of the embryo incurved in a large circle. Fresli or brackish waters, 

 Mass, to Ont. and Va. June, July. Propagating chiefly by bur-like winter- 

 buds formed by hardened abbreviated branches and indurated bases of leaves. 

 (Nat. from Eu.) 



19. P. zosterifblius Schumacher. Stem branching, icing-flattened; leaves 

 linear and grass-like (0.5-2 dm. long, 2-4 mm. wide), abruptly pointed, with many 

 fine and 3 larger nerves ; stipules oblong, very obtuse ; spikes cylindrical, 12-15- 

 flowered, not half so long as the peduncle ; fruit obliquely obovoid, 3.5-4.5 mm. 

 long, somewhat keeled and with slight teeth on the back, the sides not im- 

 pressed, the face arching and terminated by the short style ; summit of the 

 large embryo lying transverse to the fruit. Still and slow-flowing waters, N. B. 

 to B. C., s. to N. J., the Great Lake region, la., etc. June-Aug. Freely propa- 

 gating by large winter-buds. (Eurasia.) 



20. P. acutifblius Link. Similar ; leaves many-nerved, sharp-acuminate ; 

 spikes globose, 4-8-flowere d ; fruit conspicuously crested, the sides flat. Col- 

 lected at Lancaster, Pa., by Mnhlenberg nearly a century ago ; not since found 

 in Am. July, Aug. (Eurasia, Austr.) 



21. P. Hillii Morong. Stem slender, widely branching, Jlattish ; leaves 

 linear, acute (2.5-6.5 cm. long, 1-2.2 mm. wide), 3-nerced, the lateral nerves 

 delicate and near the margin ; stipules whitish, striate, obtuse; spikes capitate 

 (3-0-fruited), on short spreading or recurved peduncles ; fruit as in the last, but 

 the sides rounded. Lakes and ponds, Ct. to Pa., Mich., and Ont. July, Aug. 



22. P. obtusif61ius Mertens & Koch. Stem flattened, very branching ; leaves 

 linear, tapering toward the base, obtuse and mucronate, 1.5-3.5 mm. broad, 

 3(rarely 5 or ~)-nerved, bearing 2 large translucent glands at base ; spike con- 

 tinuous, 5-8-flowered (8- - 24-f raited, most of the carpels maturing), about the 

 length of the peduncle ; fruit ovoid, apiculate with the style, not keeled when 

 fresh, upper portion of embryo coiled inward and lying transverse to the fruit. 

 Clear streams and ponds, e. Que. to Athabasca, s. to e. N. Y., Pa., Mich.. 

 Wise., Minn., and Wyo. July-Sept. Freely propagating by large winter-buds. 

 (Eurasia.) 



23. P. FriSsii Rupr. Resembling no. 25 ; stem more flattened and les 

 branching; leaves broader (1-3 mm. wide), ^-7-nerved; winter-buds abundant; 

 stipules conspicuous, white-hyaline ; glands small and dull ; spikes interrupted, 

 in fruit 0.8-1.6 cm. long. (P. mucronatus Man. ed. 6, notSchrad.?) Local, 

 P.E.I, to B.C., s. to Ct., N. Y., Mich., Wise., Minn., and N. Dak. July, Aug. 

 (Eu.) 



