674 NAIADACEZ POTAMOGETON 
7 POTAMOGETON L. Sp. 126. 
Submersed aquatic herbs with slender jointed branching stems, 
mostly alternate leaves with scarious stipules and perfect flowers 
in peduncled axillary spikes: Perianth herbaceous, of 4 narrow 
valvate segments. Stamens 4, opposite to the segments; with 
nearly sessile 2-celled anthers. Ovaries usuallv 4 and sessile, 
with oblique depressed nearly sessile stigmas and solitary ascend- 
ing campylotropous ovules. Fruit somewhat compressed, ovate, 
drupe-like, with a crustaceous nutlet within. Seed with mem- 
branous testa and strongly curved or spiral embryo. 
* Floating leaves more or less coriaceous, with a dilated petioled 
blade, different in form from the thinner submerged ones: stipules 
free: spikes cylindrical, mostly dense, not interrupted. 
P. natans L. Sp. 126. Stems 1-4 feet long, simple or sparingly bran- 
ched: floating leaves thick, ovate-elliptic to lanceolate, acutish, slightly 
cordate at base, usually 2-3 inches long, mostly shorter than the petiole, 
21-29-nerved: stipules long and conspicuous, acute or acuminate; unpre 
submersed leaves often with a small lanceolate blade, the lower reduced to 
petioles: peducles stout, bearing an emersed spike 1-2 inches long: fruit 
turgid, obliquely obovate, acute, 2 lines long: nutlets with a small deep 
pit on each side: embryo nearly circular. In ponds and ditches, Alaska to 
California and across the Continent: olso in Europe and Asia. 
P. amplifolius Tuckerm. Am. Journ. Sci. (II) vi, 225. Stems often 
stout, simple: floating leaves elliptic to oblong-lanceolate, acute, mostl 
rounded or slightly cordate at base, 2-4 inches long, 30-50-nerved, on peti- 
oles about as long as the blade; stipules large and conspicuous: submerged 
leaves often very large, mostly falcate and somewhat undulate, acute, at- 
tenuate to a usually short petiole: spikes thick and often dense, 1-3 inches 
long, on very short peduncles: fruit over 2 lines long, 3-keeled, with a 
broad stout beak: sides of the nutlet not pitted: embryo slender, the coty- 
ledon incurved. In ponds and streams, Brit. Columbia to California and 
the Eastern States. 
P. puleher Tuckerm. Am Journ. Sci. xlv, 38. Stems simple, terete, 
black-spotted, 1-2 feet long: floating leaves usually massed at the top on 
short. lateral branches, ovate or round-ovate, subcordate, 2-5 inches long, 
many-nerved : petioles about as thick as the stem, 2-4 inches long, spotted: 
submerged leaves of two kinds, the uppermost lanceolate, long-acuminate, 
undulate, 3-8 inches long, 6-8 lines wide, tapering into a short petiole, the 
lowest much thicker, spatulate, oblong or ovate, on petioles 14-4 inches 
long: stipules 2-carinate: spikes dense, long-peduncled: fruit adout 2 lines 
long. turgid, tapering into 4 stout apical style, the back sharply 3-keeled: 
embryo coiled. In ponds, Idaho to Main and Georgia. 
P. Nuttallii Cham. & Sch. Linn. ii, 226. P. Claytonii Tuckerm. 
Stems compressed, mostly simple, 2-6 feet long: floating leaves narrowly 
oblong to elliptic, 1-3 inches long, 11-17-nerved, obtuse or acutish, attenu- 
ate below into a flattened petiole usaally shorter than the blade: stipules 
sheathing, soon deciduous, an inch or less long: submerged leaves very 
thin linear, 2-5 inches long, 5-nerved, with a close cellular reticulation 
between the middle nerves: spikes 6-12 lines long, on short stout peduncles; 
fruit obovate, 3-keeled, slightly apiculate, 1-14 lines long: nutlets slight] 
depressed on the sides: embryo coiled nearly 14 times. In ponds anc 
streams, California to Alaska and the Eastern States, 
P. alpinus Balbis Miso. Bot. 13. (1804), P. rufescens Schrad. (1815.). 
