POTAMOGETONACEAE. 15 



24. POTAMOGETON. Pondweed. 



Leaves alternate or the uppermost opposite, often of two 

 kinds, the submersed mostly linear, the floating lanceolate, 

 ovate or oval ; spathes enclosing the young buds usually perishing 

 soon after expanding; flowers small, perfect, spicate, green or red; 

 parts of flower in fours; ovaries 4, sessile, distinct, 1-celled, 

 1-ovuled. 



Leaves all submersed, linear. 



Stipules free from the blades; fruit 1.5-2 mm. long. P. californicus. 



Stipules united to base of blades; fruit 3-4 mm. long. P. pectinatus. 



Leaves not all submersed; floating ones broad. 



Submersed leaves ribbon-like, linear. P. epihydrus. 



Submersed leaves lanceolate. 



Floating leaves cordate at base. P. pulcher. 



Floating leaves rounded or tapering at base. 



Floating leaves 30-50 nerved. P. amplifolius. 



Floating leaves 10-25 nerved. P. americanus. 



Potamogeton californicus (Morong) Piper. Stems slender, much branched, 

 flattened or somewhat winged, 30-50 cm. long, wholly submersed; leaves 

 linear, sessile, 2-5 cm. long, 0.2-1 mm. wide, 3-5-nerved, the midvein thick; 

 peduncles erect, club-shaped; spike containing 6-12 globose fruits, these 

 crested on the back, angled in front, short-beaked, about 2 mm. long. Ponds, 

 common. 



Potamogeton pectinatus L. Stems filiform, branched, 30-90 cm. long; 

 leaves narrowly linear, attenuate to the apex, 1-nerved, 2-10 cm. long; pe- 

 duncles slender; flowers in whorls; fruit obliquely obovoid, compressed, turgid, 

 3.5—4.5 mm. long; style straight or nearly so. In ponds, not rare. 



Potamogeton epihydrus Raf. (P. nutlallU C. & S.) Stems simple or 

 branched, compressed, 60-120 cm. long; floating leaves oblong, obtuse or 

 acutish, attenuate into a short petiole; submersed leaves numerous, linear, 

 thin, 5-7-nerved, with a coarse cellular reticulation between the inner nerves; 

 stipules short, obtuse; spikes 1-4 cm. long, on stout peduncles; fruit obovoid, 

 apiculate, 2-3 mm. long, 3-keeled when dry. Waitsburg, Horner. 



Potamogeton pulcher Tuckerm. Stems mostly simple, slender, terete, 

 black-spotted, 30-70 cm. long; floating leaves large, ovate, somewhat cordate 

 at base, 25-37-nerved, large, 5-10 cm. long; submersed of two kinds, the upper 

 ones very thin, 10-15-nerved, lanceolate, long-acuminate, the lowermost oval 

 or oblong and thicker; peduncles as thick as the stem, 5-10 cm. long; spikes 

 2—4 cm. long; fruit 4—4.5 mm. long, turgid, beaked, 3-keeled. Reported from 

 Lake Tesemini (Spirit Lake), Idaho. 



Potamogeton amplifolius Tuckerm. Stem stout, simple or branched ; floating 

 leaf-blades oblong-oval, acute, rounded at the base, 5-10 cm. long, on petioles 

 one to two times as long; submersed leaves mostly linear-lanceolate to lan- 

 ceolate, the uppermost frequently oval or oblong; stipules large, 5-10 cm. long, 

 spike stout, dense, 2-i cm. long, on stout peduncles; fruit large, 4-5 mm. long, 

 with a broad beak. Pullman, rare. 



Potamogeton americanus C. & S. (P. lonchitis Tuckerm.) Stems slender, 

 flaccid, branched, 50-100 cm. or more long; floating leaves narrowly elliptic, 

 pointed at each end, 5-10 cm. long, many-nerved, narrowed at the base into 

 a petiole about as long; submersed leaves linear; stipules narrow, 3-8 cm. long; 

 spike dense, 2-4 cm. long, on rather stout peduncles; fruit about 3-4 mm. long. 

 In ponds and pools, not common. 



