POTAMOGETON NAIADACEZ 675 
Stems simple or branched, 1-2 feet high, somewhat compressed: floating 
leaves often wanting, rather thin, 11-17-nerved, narrowly oblong-elliptic 
or oblanceolate, 2-4 inches long, acutish, attenuate into a very broad short 
. petiole; submerged leaves as large as the floating ones, sessile or nearly so, 
mostly attenuate, narrowly oblong-lanceolate, 3-12 inches long, 3-6 lines 
wide: stipules broad, usually acuminate, 6-12 lines long or more: spikes 
1-2 inches long, rather slender, on stout often elongated peduncles: fruit 
round-obovate, 144 lines long, compressed acutely margined, beaked by the 
rather long style: nutlets pitted on both sides: embryo nearly circular. 
In alpine ponds, Brit. Columbia to California and the Eastern States, also 
in Europe. 
P. lonchites Tuckerman Am. Journ. Sci. (IL) vi, 226. Stems rather 
slender, branching, terete, 3-6 feet long: floating leaves thickish, 11-23- 
nerved, long-elliptical to oblong-lanceolate, usually 2-4 inches long, 9-15 
lines wide, acute or acutish, rather abruptly narrowed into a petiole, usu- 
ally longer than the blade; submersed leaves thinner, mostly linear-lance- 
olate, 3-12 inches long, 2-12 lines wide, attenuate at base, the lower sessile: 
stipules 1-4 inches long: spikes dense, 1-2 inches long, on stout peduncles: 
fruit obliquely obovate, 1-2 lines long, carinate, acute: nutlets somewhat 
3-keeled, the sides scarcely impressed : cotyledons incurved above the base 
of the slightly incurved embryo. In ponds and slow streams, Washington 
to California and the Eastern States. 
P. heterophyllus Schreb. Special Fl. Lip. xxi, 1771. Stems very 
slender, branching: floating leaves rather thin, 9-15-nerved, oblong-ellip- 
tic, acutish, 1-2 inches long, rounded or cuneate at base, on slender peti- 
oles mostly as long or longer than the blade: stipules broad, obtuse, about 
an inch long: submersed leaves linear-lanceolate, 1-2 inches long, 1-3 lines 
wide, acute or acuminate, narrowed at base: spikes about an inch long, 
rather loose, on stout often elongated peduncles: fruit round-obovate, a 
line long, acute, scarcely keeled: embryo stout, incurved. In different 
forms throughout most parts of North America: also in Kerope. 
* * Leaves all submerged and uniform, thin and dilated, numer- 
ous, mostly sessile: spikes dense, on stout peduncles. 
P. prelongus Wulf. in Rom. Arch. iii, 331. Stems stout, elonga- 
ted, branching and flexuous above, usually growing in deep water, some- 
times 8 feet long: leaves often lanceolate, 2-10 inches lobe: 6-12 lines 
wide, obtuse and somewhat cucullate at the apex, rounded and clasping at 
base, undulate-serrate: stipules white and conspicuous, 6-12 lines long: 
peduncles often much elongated; fruit semicircular, 2 lines long, acutely 
keeled, prominently beaked: embryo slender, the cotyledons pointing to 
the base of the radicle. In deep water, Brit. Columbia to California and 
the Eastern States. 
P. perfoliatus L. Sp. 126. Stemsslender, not flexuous, 2-4 feet high, 
branching: leaves broadly cordate to cordate-lanceolate, 6-18 inches long, 
obtuse to acute, clasping at base: stipules small and not persistent: spikes 
8-12 lines long, often flowering and fruiting under water: fruit obliquely 
obovoid, nearly 14 lines long, obtusely keeled, beaked by the short slender 
style: embryo slightly incurved or with the apex pointing directly toward 
the base. In streams and ponds, California to Brit. Columbia and across 
the continent. ; 
Var. Richardsonii A. Bennett Britten’s Journ. Bot. xxvii, 25. 
Leaves 1-5 inches long, 4-8 lines wide at the broadened amplexicaul base, 
often curved inward at the apex, 13-23-nerved: fruit about 2 lines long, 
14% lines thick. In streams and ponds, Oregon to California and Delaware. 
P. zosterefolius Schum. Enum. Pl, Saell. 50. Stems much flattened, 
