BRITISH FLORA 



rivers, and streams, and the plant is common in 

 deep water. The plant has the pondweed habit. 

 The stem is stout and long. The plant is shining 

 and glistening. The leaves are large, more or 

 less stalkless, translucent, transparent. They are 

 mainly submerged, oval, oblong, or lance-shaped, 

 linear, blunt-pointed, wavy, with small serratures, 

 many -nerved. The upper leaves are leathery, 

 opposite, floating. The stipules are winged or 

 keeled on the back, large, and long. The flowers 

 are in a stout, cylindrical, dense spike. The 

 flower-stalks vary in length, are swollen upwards, 

 and are as long as the spikes. The fruit is 

 rounded on the back, keeled when fresh, the 

 drupelets being small and turgid, with a short, 

 blunt beak. The plant is 3-6 ft. long, flowering 

 from June to September, and is a herbaceous 

 perennial. 



Potamogeton decipiens, Nolle. The habitat of 

 this plant is streams and canals, and the plant is 

 very rare. The stem is long, much-branched. 

 The leaves are membranous, transparent, stalk- 

 less, more or less rounded, or oblong to lance- 

 shaped, not hooded, blunt, blunt-pointed, more or 

 less entire, wavy at the end, the uppermost more 

 or less stalkless. The stipules are short, not, or 

 scarcely, winged. The flowers are in a dense 

 spike 1-2 in. long. The flower-stalks are equal, 

 stout. The fruit is as in the last but smaller. 

 The plant is in flower in July, and is a herbaceous 

 perennial. 



Potamogeton griffithii, A. Benn. ( = P. alpinus X 

 P. pr<elongus). The stem of this plant is branched, 

 round in section. The submerged leaves are more 

 or less clasping, strap-shaped, wavy, hooded, 

 membranous, with a concave tip, ii-nerved, with 

 4-5 fainter nerves near the midrib. The upper 

 leaves are long-stalked, inversely lance-shaped, 

 tapered into the leaf-stalk, and are ij-iy-nerved, 

 blunt, more or less leathery. The stipules are 

 long, narrow, blunt. The flowers are in a dense 

 spike. The flower-stalks are slender, not so long 

 as the upper leaves. The young fruit is ovoid, 

 the beak terminal from the ventral face. The 

 plant is in flower in July and August, and is a 

 herbaceous perennial. 



Potamogeton zizii^ Roth ( = P, angustifolius, 

 Presl). The habitat of this plant is lakes and 

 rivers. The stem is long, much-branched. The 

 leaves are nearly all submerged, membranous, 

 transparent, narrow to lance - shaped, oblong, 

 blunt -pointed, wedge-shaped, narrowed below, 

 wavy near the end, with small teeth bent back. 

 The floating leaves are inversely ovate-oblong, 

 more or less leathery. The stipules are long, 

 broad, with a broad, double keel. Sometimes 

 there are aerial leaves, short -stalked, leathery, 

 oblong, acute both ends. The flowers are in a 

 short spike. The stipules are very long, straight, 

 swollen upwards, thicker than the stem, longer 

 than the leaves, terminal. The drupelets are 

 rounded, with 3 keels. The plant flowers in July 

 and August, and is a herbaceous perennial. 



Long -stalked Pondweed (Potamogeton prce- 

 longus, Wulf.). The habitat of this pondweed is 



lakes and deep rivers, ditches chiefly in the East. 

 The stem is round in section, greenish - white, 

 robust, growing in deep water. The leaves are 

 transparent, half-clasping, linear to oblong, blunt, 

 hooded at the end, entire, with a swollen midrib, 

 with parallel veins, the upper leaves opposite. 

 The veins are numerous and close. The stipules 

 are not winged, blunt, large. The flowers are in 

 a dense spike. The flower-stalks are not thickened 

 upwards, stout, equal, very long. The fruit is 

 strongly acutely keeled on the back when fresh, 

 or winged when dry. The plant flowers from 

 May to July, and is a herbaceous perennial. 



Potamogeton salicifolins, A. Benn. ( = P- lithuani- 

 CHS, Gorski). The habitat of this species is rivers. 

 The plant is not much branched. The stem is 

 slender, round in section. The leaves are trans- 

 lucent, submerged, half-clasping, lance-shaped, 

 acute or more or less so, entire, 3-nerved, with 

 numerous secondary nerves. The stipules are 

 blunt. The flowers are in a short spike. The 

 flower-stalks are not enlarged upwards. The 

 drupelets, when dry, are flattened, rounded, blunt. 

 The British plant does not fruit. It flowers in 

 July, and is a herbaceous perennial. 



Perfoliate Pondweed (Potamogeton perfoliatus, 

 L.). The habitat of this species is ponds, lakes, 

 rivers, and streams. The stem is stout, round in 

 section, slightly branched, regularly forked above. 

 The leaves are transparent, heart-shaped to ovate 

 or lance-shaped, clasping, not hooded, the tip flat, 

 blunt, or more or less acute, entire, 5~9-nerved. 

 The upper leaves are opposite, translucent. The 

 stipules are small, more or less acute, not persis- 

 tent. The flowers are in a dense spike. The 

 flower-stalks are thick, equal, terminal, and in the 

 forks short, stout, not thickened upwards. The 

 perianth-segments have a long claw. The fruit is 

 rounded on the back when fresh, keeled when dry. 

 The plant is in flower between June and September, 

 and is a herbaceous perennial. 



Curled Pondweed (Potamogeton crispus, L.). 

 The habitat of this species is ponds, ditches, 

 streams, &c. The stem is flattened, slender, 

 repeatedly forked. The leaves are in 2 rows, 

 transparent, crisped at the margin, half-clasping, 

 oblong, linear, blunt, stalkless, wavy, coarsely 

 toothed, 3-nerved, close, spreading, bent-back. 

 The stipules are small, blunt, and do not persist. 

 The flowers are few, 6-8, in a loose small spike. 

 The flower -stalks are curved, tapered upwards, 

 stout or slender, equal, long. The fruit is keeled 

 on the back when dry, with a long beak as 

 long as the drupelets, which are obliquely ovoid, 

 flattened. The plant is in flower in July and 

 August, being a herbaceous perennial. 



Dense Opposite - leaved Pondweed (Pttlnmo- 

 geton densus, L.). The habitat of this species is 

 ponds, shallow streams, ditches. The stem is 

 brittle, slender, repeatedly forked. The leaves 

 are all submerged, opposite, the margins rolled 

 in in bud. They are in 2 rows, elliptic, lance- 

 shaped or ovate to heart-shaped, transparent, 

 clasping, with a few teeth, 3-5 nerved, close, 

 bent-back, acute, keeled, and the nodes of those 



