Part 178 (1/2)

9. P. fluitans, Roth. Stem often branching below; _floating leaves thinnish, lance-oblong or long-elliptical_, often acute, _long-petioled_, 17--23-nerved; _submersed leaves very long_ (3--12', by 2--12” wide), _lanceolate and lance-linear_, 7--15-nerved, coa.r.s.ely reticulated; peduncles somewhat thickened upward; 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 circularly in-curved. (P. lonchites, _Tuckerm._)--In streams or rarely in ponds, N. Brunswick to N. J., west to Minn. and Iowa. Aug., Sept. (Eu.)

10. P. pulcher, Tuckerm. Stem simple, black-spotted; _leaves of three kinds_; floating ones becoming very large (4 by 3'), _roundish-ovate and cordate or ovate-oblong_, 25--37-nerved, _all alternate; upper submersed ones (3--5) usually lanceolate_, acute at base and very long-ac.u.minate, 10--15-nerved, very thin, cellular each side of the midrib, undulate, short-petioled; _lowest_ (2--4 near the base of the stem) _thicker, plane, 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, distinctly 3-keeled when fresh, sharply so when dry; nutlet with two deep dorsal furrows, and a sinus below the angle in front; sides flat; embryo circularly much incurved above.--Ponds, Vt. to Ga. and Mo. July, Aug.

11. P. ampliflius, Tuckerm. Stems simple, of very variable length; _floating leaves_ (sometimes wanting) large, _oblong or lance-ovate_, sometimes slightly cordate at base, abruptly acutish, 30--50-nerved, on _rather long petioles_; submersed leaves often very large (reaching 7'

by 2'), lanceolate or oval, acute at each end, _usually much recurved, undulate_, mostly on short petioles; _stipules very long and tapering to a point_, soon becoming loose; peduncles thickened upward, in deep water much elongated; fruit very large (over 2” long), rather obliquely obovate, 3-keeled, with a broad stout beak; nutlet slightly impressed on the sides; upper part of the embryo curved into a ring.--Ponds and rivers, N. Eng. to N. J., west to Minn. and Kan. Aug., Sept.

12. P. Illinoensis, Morong. _Stem stout, branching_ towards the summit; floating leaves opposite, oval or ovate (2--5' long by 1--2' broad), 19--25-nerved, rounded or subcordate at base, with a short blunt point at apex, on short petioles, _submersed leaves rather few, oblong-elliptical_, acute at each end, _usually ample_ (largest 8' by 1'); _stipules coa.r.s.e, obtuse, strongly bicarinate_ (2' long); peduncles often cl.u.s.tered at the summit (2--4' long), thickening upward; _fruit roundish-obovate_ (1--2” long), 3-keeled on the back, middle keel prominent; nutlet flattened and slightly impressed on the sides, obtuse or pointed at base; apex of embryo directed transversely inward.--Streams and ditches, western N. Y. to Ill., Iowa, and Minn.

Very near the last.

13. P. heterophllus, Schreb. _Stem slender, very branching_ below; floating leaves mostly thin, variable, but with a short blunt point, 9--15-nerved, usually 1--2' long and 6--9” wide; submersed ones usually lanceolate or linear-lanceolate, ac.u.minate or cuspidate, narrowed toward the base, about 7-nerved on the stem and 3-nerved on the branches; upper ones petioled, lower sessile; _stipules obtuse_, loose; peduncles somewhat thickened upward; fruit small, roundish, compressed, scarcely keeled; embryo annular above. (P. gramineus, _Fries_.)--Still or flowing water, common. Varies exceedingly in its submersed leaves, peduncles, etc.; the var. GRAMINIFLIUS (Fries), growing in rapid streams, with stems much elongated and less branched, and the flaccid submersed leaves 2--7' long by 2--10” wide.

Var. (?) myriophllus, Robbins. Sending up from running rootstocks many short repeatedly dichotomous and densely leafy stems; fertile stems very slender; floating leaves small, delicate, lance-oblong, on long filiform petioles; submersed stem-leaves larger, early peris.h.i.+ng; those of the branches (deep-green) linear-oblanceolate, very small (--1' long), acute, sometimes minutely serrulate; spike slender, loosely-flowered, much shorter than the thickened peduncle.--Apponaug Pond, R. I., without fruit.

13^a. P. Zizii, Mert. & Koch. Resembling P. lucens, but smaller, much branched at base; _upper leaves coriaceous or subcoriaceous, long-petioled_ and _sometimes emersed_, the others subsessile, all usually numerous, undulate and _s.h.i.+ning_; peduncle elongated. (P.

lucens, var. minor, _Nolte_. Also P. gramineus, var. (?) spathulaeformis, _Robbins_; P. spathaeformis, _Tuckerm._; ”P. varians, _Morong_.”)--N. Eng to Fla., and westward. Connecting with the next section. (Eu.)

-- 2. _Leaves all submersed and similar, mostly sessile, membranaceous and dilated, lanceolate, oblong, or oval; stipules obtuse, becoming loose._

14. P. lucens, L. Stem thick, branching, sometimes very large; _leaves more or less petioled_, oval or lanceolate, _mucronate_, often rough serrulate, _frequently s.h.i.+ning_; peduncles often elongated; _fruit_ roundish and compressed, _with obtuse margins, slightly keeled_; embryo circularly incurved above.--Ponds, N. Eng. to Fla., west to the Pacific.

Aug., Sept. (Eu.)

Var. (?) Connecticutensis, Robbins. Stem flexuous; _leaves_ all submersed, nearly sessile, lanceolate, _ac.u.minate, crisped, not s.h.i.+ning nor serrulate; fruit larger, distinctly keeled_; nutlet thick and hard.--Lake Saltonstall, East Haven, Conn.

15. P. praelongus, Wulf. Stem very long, branching, flexuous; _leaves_ lance-oblong or lanceolate (sometimes 7' long), _half-clasping, obtuse with a boat-shaped cavity_ at the extremity, thence splitting on pressure; stipules scarious, very obtuse; spikes rather loose-flowered; _peduncles very long_ (sometimes reaching 20'); _fruit_ obliquely obovate, compressed, _sharply keeled_ when dry; style terminating the nearly straight face; curve of the embryo oval and longitudinal.--Ponds and large rivers, N. Scotia to Ma.s.s., west to Minn. and Iowa. Sept., Oct.--Stem white; foliage bright green. (Eu.)

16. P. perfoliatus, L. Stem branching; _leaves...o...b..cular, ovate or lanceolate from a cordate-clasping base_, usually obtuse and often minutely serrulate; peduncles short, cylindrical; _fruit_ irregularly obovate, _obtusely margined_; embryo incurved in an oval.--Ponds and slow streams, common. N. Scotia to Fla., west to Minn. and Iowa. Sept., Oct. (Eu.)

Var. lanceolatus, Robbins. Larger; _leaves long-lanceolate_ from a cordate clasping base and _ac.u.minate_, wavy, 3--4' long; _peduncles thickened upward_.--Same range as the species, and extending west to the Pacific.

17. P. crispus, L. _Stem compressed; leaves linear-oblong_, half-clasping, obtuse, _serrulate, crisped-wavy, 3-nerved; fruit long-beaked_; upper portion of the embryo incurved in a large circle.--Flowing and stagnant waters, Ma.s.s. to N. J. and Va., west to western N. Y. June, July. (Eu.)

18. P. Msticus, Morong. _Stem very slender_ and irregularly branching, nearly filiform (1--3 high); _leaves oblong-linear_ (--1' long by 2--3” wide), 5--7-nerved, _finely undulate and entire, obtuse or bluntly pointed, abruptly narrowing at base, sessile or partly clasping_; spikes few, capitate (4--6-flowered). on erect peduncles (1--2' long); fruit (immature) obovate, small (hardly ” long), _obscurely 3-keeled on the back_, a little beaked by the slender recurved style.--Mystic Pond, Medford, Ma.s.s.

-- 3. _Leaves all submersed and similar, mostly membranaceous and sessile, linear or setaceous._

[*] _Stipules free from the sheathing base of the leaf._

19. P. zosteraeflius, Schum. _Stem branching, wing-fattened; leaves_ linear and gra.s.s-like (commonly 4' by 1”), _abruptly pointed, with many fine and 3 larger nerves_; stipules (seen young) oblong, very obtuse; _spikes cylindrical_, 12--15-flowered, _not half as long as the peduncle_; fruit obliquely obovate, somewhat keeled and with slight teeth on the back, the sides not impressed, the face arching and terminated by the short style; _summit of the large embryo lying transverse to the fruit_. (P. compressus, _Fries_; not _L._?)--Still and slow-flowing waters, N. Eng. to N. J., Iowa, and Minn. Aug., Sept. (Eu.)

20. P. Hillii, Morong. Stem slender, _widely branching, flattish_; leaves linear, _acute_ (1--2' long by --1” wide), _3-nerved_, the lateral nerves delicate and near the margin; stipules whitish, striate, obtuse (3--5” long); _spikes capitate_ (3--6-fruited), _on short spreading or recurved peduncles_; fruit as in the last.--Mich. and western N. Y.

21. P. obtusiflius, Mertens & Koch. _Stem flattened, very branching; leaves_ linear, tapering toward the base, obtuse and mucronate or very acute, _3- (rarely 5-) nerved; stipules elongated_, very obtuse; _spike ovate, continuous_, 5--8-flowered, _about the length of the peduncle_; fruit oval, apiculate with the style, not keeled when fresh, _upper portion of embryo_ coiled inward and _lying transverse to the fruit_.--Slow streams and ponds, Canada and N. Eng. to western N. Y. and Mich. Sept., Oct. (Eu.)

22. P. pauciflrus, Pursh. _Stem filiform, flattish and very branching; leaves narrowly linear_ (1--2' long and seldom ”

wide), acute, _obscurely 3-nerved; stipules obtuse; spikes_ capitate, 1--4- _(usually 2-) flowered_, on short club-shaped peduncles; _fruit roundish-lenticular_; the _back_ more or less _crested_; upper portion of the embryo incurved in a circle.--Still or stagnant waters, N.

Brunswick to Ga., Iowa, Minn., and westward.

Var. Niagarensis, Gray. Stem often longer (1--3); leaves larger (1--3' long by 1” wide or less), 3--5-nerved at base, very acute and mucronate, narrowed to the subpetiolate base. (P. Niagarensis, _Tuckerm_.)--Running water, Great Lakes to S. C.; also in Cal.