486 NAIADACIi^E. (I'ONDWKKD FAMILY.) 



about equalling the rather dilaled petioles, with 5 - many nerves beneath deeply 

 impressed ; upper submersed leaves either witli or without a lanee-oblong or 

 broad-linear prui)er blade; the numerous lower ones narrow-linear, tapering 

 towards the obtuse apex ('i' - 1^' long, i"-'i' wide) ; stipules early laeeratc ; 

 suimtrsid Jhiicers tistudli/ solitary on verif sliorl ertct peduncles; sliell-slmpedfrtdt with 

 the back either a-imjed and with 4-5 distinct letth or wiiajless and entire; embryo 

 coiled \[ turns. — Uivers, and even far up snuill streams, in company witli the 

 Ko. 3, or rarely with the following, Maine (J. Blake) to Lake Superior and 

 Virginia. June -Aug. — Stem less slender than the next. 



6. P. hybl'idus, Miehx. Floating leaves varying from oval to lance- 

 oblong ; (the largest 10" long and 6" wide), often acute, longer than the JH iforni 

 \)etioles, with about 5-7 nerves beneath deeply impressed ; submersed leaves very 

 numerous, alniost setaceous, (l'-3' long, very rarely ^" wide) ; stipules oljtuse; 

 mbmersed spikes 1 -4-Ho\vered, their fieduncles (of their own langth) Jie(jueiitli/ 

 recurved ; J'ruit minute, about 8-louthed on the margin; embryo coiled l^ turns. (P. 

 diversifolius, Barton. P. setaceus, Pursli.) — Shallow stagnant waters. June - 

 Aug. — Emersed spikes 4" to (in var. spicatus, Enijdm.) 7" long. 



* * Submersed leaves lanceolate, rarely oral or linear, membranaceous. 



7. P. rufescens, Schrader. Stem simple, floating leaves (often wanting, 

 p. obrutus, Wood) rather thin, wedge-oblunceolute, narrowed into a .short petiole, 1 1 - 

 17-ncrved; submersed leaves almost sessi'fe, lanceolate and lance-oblong, smooth 

 on the margin, fewer-nerved ; stipules broad, hyaline, obtuse, ui)])cr ones 

 acuminate; fruit obovate, lenticular, pitted when immature, with an acute 

 margin and pointed with the rather long style ; embryo incompletely annular. 

 — Rivers and streams, New England to Pennsylvania, Illinois, and especially 

 northward. — Aug. - Sept. — Spike often somewhat compound ! (Eu.) 



8. P. lonchites, Tuckerman. Stem often branching below ; ^floating 

 leaves thiimish, lance-oblong or long-elliptical, often acute, loiig-petiuled, 17-2-3- 

 nerved; submersed leav&i very long (.3' -12', by 2"- 12" wide), lanceolate and 

 lanre-linear, 7-15-nerved, coarsely reticulated ; peduncles somewhat thickened 

 upwards ; fruit obliquely obovate, obscurely 3-keeled when fresh and distinctly 

 so when dry, the middle one winged above and sometimes with 3-5 shallow 

 indentations; the rounded slightly curved face surmounted by the short style; 

 nutlet with the sides scarcely impressed ; upper part of the embryo circulirly 

 incurved. (P. Americanus, Chamisso?) — Rivers and ponds, New England to 

 Illinois. Aug., Sept. — More slender than the very similar P. fliiitaus of 

 Europe, its leaves longer petioled, the floating ones more abrupt at the base ; 

 stipules not bicarinate. Cham i.sso's name of this and Xo. 3 merely provisional. 



9. P. pulcher, Tuckerman. Stem simple, black-spotted ; leaves of three 

 kinds; floating ones becoming very large (4^' by 3h') roundish-ovate and cordate 

 or ovate-oblong, 2!i- 37 -nerved; idl alternate; upper submersrd ones (3-5) usually 

 lanceolate, acute at the base and very long-acuminate, 10- 15-ncrvc(l, very thin, 

 cellular each side of the midril), undulate, short-jietioled ; lowest (2-4 near the 

 base of the stem) thicker, jilane, oval or oblong with a rounded base, or spatulate- 

 oblong, on longer petioles; stipules rather short and obtuse; peduncles thicker 

 than the stem ; fruit with a rounded back and angular face, pointed with the 



