LAKES, RIVERS, DITCHES, ETC. 



that are more or less opposite are confluent with 

 an overlapping- base. There are no stipules except 

 on the upper leaves. The spike is loose, short, 

 shortly-stalked, with few flowers, 3-6, bent-back 

 ultimately. The flower-stalks are as long- as the 

 leaves, bent-back at length. The sepals are tri- 

 angular. The drupelets are flattened, with a thin 

 pericarp, more or less round, with a sharp keel, 

 and a short beak which is bent-back. The plant 

 flowers between July and September, and is a 

 herbaceous perennial. 



Sharp-leaved Pond weed (Potamogeton zosteri- 

 folius, Schum. = P. compressus, L.). The habitat 

 of this species is rivers, lakes, streams. The stem 

 is flattened, winged, broad, with long internodes. 

 The leaves are all submerged, alternate, linear, 

 ligulate, with a narrow point, abrupt, with 3-5 

 primary and numerous, close, parallel, intermediate 

 veins, half-clasping-. The stipules are free, large, 

 with a narrow point. The flowers are numerous 

 in a cylindrical spike, 10-15. The sepals are trans- 

 versely oval. The flower-stalks are longer than 

 the spike. The drupelets are flattened, inversely 

 ovate, 3-keeled, the inner edge rounded, with con- 

 vex faces. The style is terminal, forming- a beak 

 in fruit. The plant flowers in July and Aug-ust, 

 and is a herbaceous perennial. 



Potamogeton acutifolius, Link. The habitat of 

 this species is lakes and ditches, marsh or fen 

 ditches. The stem is flattened. The leaves are 

 all submerged, alternate, linear to ligulate, long- 

 pointed, with 3 principal and many close parallel, 

 slender, intermediate veins. The stipules are 

 lance-shaped, acute. The flowers are in a very 

 short spike, which is ovate, as long- as the stalks. 

 The sepals are rhomboidal. The stalk is very 

 short. The drupelets are convex, the inner edge 

 straight, with a tooth near the base, inversely 

 ovate, flattened, keeled. The styles are hooked, 

 and continue the inner edge of the fruit, being 

 ventral, and bent-back. The plant flowers from 

 June to August, and is a herbaceous perennial. 



Potamogeton obtusifolius, Mert. & Koch ( = P. 

 gramineus, Sm.). The habitat of this plant is pools, 

 ditches, ponds, and it is a rare species. The stem 

 is slender, flattened, with rounded edges, much- 

 branched. The leaves are stalkless, lance-shaped, 

 linear, more or less acute, or blunt, 3-nerved, 

 dark -green, opaque, with no veins between the 

 3 main ones. The stipules are very blunt. The 

 flowers are in a small ovoid spike, dense, con- 

 tinuous, as long as the stalk. The sepals are 

 rhomboidal, shorter than the leaves, terminal or 

 in forks. The drupelets are flattened, broadly 

 obliquely ovoid, keeled. The plant flowers in July 

 and August, and is a herbaceous perennial. 



Potamogeton friesii, Rupr. ( = F. mucronatus, 

 Schrad.). The habitat of this species is ditches, 

 canals, &c. The stem is flattened. The leaves 

 are grouped, linear, with an apiculus, 5~7-veined, 

 the lateral veins close, and nearer the margin than 

 the midrib, with no intermediate veins. The 

 flowers are in an interrupted, short, loose spike, 

 not so long as the flower-stalk. The latter is 

 flattened, club-shaped. The sepals are trans- 



ersely oval. The fruit is obliquely ovate and 

 bluntly keeled, with a short beak. The plant 

 flowers in June and July, and is a herbaceous 

 perennial. 



Potamogeton rutilus, Wolff. The habitat of this 

 species is ditches. The stem is slender, flattened. 

 The leaves are linear, the lowest blunt, the upper 

 with long narrow points, with i pair of lateral 

 veins running nearly to the apex. The stipules 

 are long, with a long tapering point. The flower- 

 stalks are two to three times as long as the rather 

 dense spike. The fruit is oblong-elliptic, obscurely 

 keeled, the inner edge nearly straight. The plant 

 flowers in July, and is a herbaceous perennial. 



Small Pond weed (Potamogeton pusillus, L.). 

 The habitat of this plant is rivers, ponds, and 

 ditches. The stem is slender, not usually flattened, 

 cylindrical, much-branched. The leaves are all 

 submerged, half-clasping, narrow, linear, usually 

 3-veined (or 5-7), with no intermediate veins, more 

 or less acute, the lateral veins half-way between 

 the midrib and margin. The stipules are small, 

 and acute. The spikes are short, loose, shorter 

 than the stalk, with 6-10 flowers. The sepals are 

 roundish to kidney-shaped. The stalks are hardly 

 flattened, slender. The drupelets are small, 

 obliquely ovoid, swollen, bluntly keeled, with a 

 stout, more or less terminal beak. The plant 

 flowers in July and August, and is a herbaceous 

 perennial. 



Potamogeton Kirkii, Syme ( = P. sparganifolius, 

 Bab.). This species is found in streams and rivers 

 and is very rare. The stem is very slender, with 

 few branches. There may be no floating leaves, 

 more or less leathery, lance-shaped, long-stalked. 

 The submerged leaves are linear, narrowed at both 

 ends, very long (2 ft.), stalkless, entire, without 

 an apiculus, few and veined, with numerous 

 parallel veins near the midrib. The leaves are 

 longer than in P. lanceolatus, green when dry, 

 and do not possess chain-like reticulations. The 

 stipules are very long, blunt, not winged. 

 The flower-stalks are slender, not club-shaped. 

 The fruit is acutely keeled. The plant flowers in 

 July and August, and is a herbaceous perennial. 



Potamogeton sturrockii, A. Benn. This has 

 been regarded as a variety or sub-species of P. 

 pusillus. The stem is slender, rather flattened. 

 The leaves are thin, blunt, 3~5-nerved, bright- 

 green, membranous. The flowers are in a short 

 spike, with a slender stalk. The drupelets are 

 small, with a short beak. 



Hair-leaved Pondweed (Potamogeton trichoides, 

 Cham. & Schl.). The habitat of this species is 

 muddy ponds and ditches. The stem is more or 

 less round in section, hairlike (hence trichoides), 

 thickened below the joints, and repeatedly branched, 

 or forked and spreading, the branches tufted. 

 The leaves are half-clasping, bristle-like, spread- 

 ing, i-veined, rigid, dark-green, with a fine point. 

 The stipules are slender, acute. The flowers are 

 in a short loose spike (3-6), curved, slender, on 

 long, not thickened stalks, longer than the spikes, 

 with large stipules. The sepals are rounded, 

 stalked. The fruit is solitary, transversely kidney- 



