148 PATAGONIAN EXPEDITIONS I BOTANY. 



b2. Stipules 2-ribbed, persisting. Submerged leaves tongue-shaped. Fruit keeled and 



beaked. lingnatus. 

 a2. Leaves all submerged. 

 b. Stipules free. 



c. Leaves narrow-oblong, serrulate, 3~7-nerved, glandless. Fruit beaked. crispus. 

 C2. Leaves linear, with 2 small basal glands. Fruit ellipsoid. 



d. Leaves 5-7-nerved. Fruit laterally 2-pitted. friesii. 



d2. Leaves 3 -nerved. Style short. pusillus. 



b2. Stipules half-adnate. Leaves setaceous. Fruit scarcely keeled. pectinatus. 



3. Stipules adnate. Leaves linear. Fruit 3-keeled. interrupts. 



i. P. CRISPUS Linn. 



Leaves 2-ranked, linear-oblong or oblanceolate, alternate or opposite, 

 sessile or amplexicaul, obtuse, crisped serrulate, the midrib often com- 

 pound with submarginal outer nerves. Stipules small, scarious, evanes- 

 cent. Peduncles 4 cm. long. Spikes 12 mm. long, bristly, having beaked 

 drupelets. Fruit ovoid ; also with winter-buds. (Britt. & Br. i, 72.) 



In ditches and sluggish streams of temperate regions. 



2. P. FLUITANS Roth. 



Like P. natans, but the submerged leaves have a lamina ; leaf-stalks flat 

 on the upper sides ; floating leaves long-petiolate, lance-ovate, attenuate 

 both ways, rounded or narrowed at the base. Rachis thicker than the 

 peduncle. 



In temperate and tropical climates, by J. B. Hatcher in S. Patagon. 



3. P. FRIESII Ruprecht. 



Stems compressed, branching. Leaves about 10 cm. by .2 mm., mostly 

 5-nerved, with 2 small glands at the base. Stipules white-hyaline, about 

 20 mm. long. Peduncles 3 cm. long ; spike interrupted ; drupelets ellip- 

 soid, dorsally grooved, with a pit on each side ; style recurved. 



(Temperate parts of Eur. and N. Am.) ; Rio Coy, Patagon. (J. B. 

 Hatcher, Jan. 16, 1897.) 



4. P. INTERRUPTUS Kitaibel. 



With running rootstock often from a small tuber ; branching fan-wise. 

 Leaves linear, 10 cm. long, 2-2.5 mm - wide, 3-5-nerved and also trans- 

 versely. Some plants with narrow i -nerved leaves. Stipules adnate to 

 leaves. Ped^mcles 25-50 mm. long. Spikes slightly interrupted. Fruit 

 obliquely obovoid, keeled. 



