20 
Floating leaves long-petiolated, obovate or elliptic, coriaceous; 
submerged leaves linear-lanceolate, narrowed at the base, translucent, 
acute; spikes dense-flowered ; peduncles somewhat thickened upwards ; 
fruits small, roundish, compressed; rhizome creeping with robust 
propagating bud-like stolons. 
Am.: West Greenl. 60°—69° 30’ (!). 
Geogr. area: North America, Iceland, Farées, Northern and Cen- 
tral Europe, Northern Siberia, Japan. 
40. P. perfoliatus L. 
Kurtz, Ber. Pfl. Jenissei, p. 148; Scheutz, Pl. vase. Jeniss., p. 163; 
BERD et 190: 
Leaves submerged, obovate or obovate-oblong with cordate- 
clasping base, obtuse, minutely serrate, tip flat; spike short, dense- 
flowered; fruits oblique-obovoid, obtusely keeled; rhizome creeping 
with robust propagating bud-like stolons. 
As.: Mouth of the Yenissei (}). 
Geogr. area: Northern North America, Iceland, Ferées, Europe, 
Northern Asia, Northern Africa, Australia. 
41. P. praelongus Wulf. 
Scheutz, Pl. vase. Jeniss. p. 163; Fl. D. t. 1687; ?P. salicifolia Wolfg., 
Scheutz, |. c. p. 163. 
Leaves submerged, oblong-lanceolate, bright-green, with half- 
clasping base and concave, boat-shaped tip; stipules very large; 
spike dense-flowered; peduncles elongating after the flowering; fruits 
oblique-obovoid, large, sharply keeled (when dried); rhizome cree- 
ping with robust propagating bud-like stolons. 
As.: Mouth of the Yenissei (!). 
Geogr. area: North America, Fer6ées, Scandinavia, Central Europe, 
Western Siberia, Japan. 
42. P. obtusifolius M. & K. 
Kruuse, Veget. i Egedesm. Skjeerg., Medd. om Groénland, XIV, 1898 
p. 361; Fl. D. t. 2107. 
Leaves linear with 3—5 nerves, obtuse, acuminate; peduncles 
short, as long as the short dense-flowered spikes; fruits oblique- 
obovoid, 3-keeled; rhizome thin, short, or wanting; propagating by 
winter-buds from the angles of the leaves on the stem. 
Am.: West Greenl. Ikamiut (68° 38’) (!). 
Geogr. area: Northern North America, North and Central Europe, 
Ural, Western Siberia, Persia. 
43. P. pusillus L. 
Lge. Consp. Fl. Groenl. p. 117 and 282; Roseny. Till. p. 710; Scheutz, 
Pl. vasc. Jeniss. p. 163; FI. D. t. 1451. 
