POND-WEED FAMILY 515 



Stalked leaves, the upper opposite, obovate to lanceolate, rounded 

 at the base, lower linear-lanceolate ; flowers in slender spikes on 

 slender stalks ; carpels very small, not keeled, red, with very short 

 beak. — Ponds ; very common. — Fl. June — September. Peren- 

 nial. 



3. P. fliiitaus. — A rare form with an unbranched stem; very 

 long, submerged leaves and rather leathery, floating ones, and a 

 jruit resembling that of P. ndtans. 



4. P. colordtus (Plantain-leaved Pond-weed). — Leaves mostly 

 submerged, long-stalked, membranous, pellucid, beautifully 

 netted, broader than those of the preceding species, elliptic- 

 orbicular, on slender stalks, with short, broad, blunt stipules ; ver^ 

 slender peduncles; carpels very small, rounded, green. — Peaty 

 ditches ; uncommon. — Fl. June — September. Perennial. 



5. P. alpinus (Reddish Pond-weed). — Stem round, unbranched, 

 I — 4 feet long ; leaves reddish, lanceolate, translucent, upper 

 short-stalked, broader, floating, or erect, rather leathery ; lower 

 submerged, sessile, many-nerved ; stipules large, blunt ; flowers in 

 stout spikes on stout stalks ; carpels ovoid, pointed, keeled, red. — 

 Ditches ; frequent. — Fl. July — September. Perennial. 



6. P. sparganiijolius (Bur-reed-leaved Pond-weed), known only 

 in Galway, has a slender, slightly-branched stem ; long leaves, the 

 upper often absent, or long-stalked, floating, and rather leathery, 

 the lower linear and many-nerved ; and long stipules. 



7. P. lanceoldtus (Lanceolate Pond-weed). — A very rare species 

 with very slender, fragile stem ; dark green, oblong, obtuse, 

 pellucid, reticulate leaves, with slender, pointed stipules ; flowers 

 in short spikes on short, slender stalks, and carpels 3-toothed. — 

 Rivers in Cambridge, Anglesea, and Down. — Fl. July — September. 

 Perennial. 



8. P. heterophyllus (Various-leaved Pond-weed). — Stem slender, 

 round, 2 — 4 feet long, much branched below ; leaves fiat, upper 

 floating, opposite, leathery, elliptic, lower submerged, lanceolate, 

 flaccid ; stipules small ; flowers numerous in dense spikes on 

 stout, axillary and terminal stalks which thicken upward ; carpels 

 small, 3-keeled, with a short beak. — Ditches ; frequent. — Fl. June 

 — September. Perennial. 



9. P. jalcdtus. — x\ dark green or reddish-green plant, with a 

 tuberous rhizome ; slender, round stem, branched below ; leaves 

 amplexicaul, entire, flat, upper leathery, with 6 opaque ribs on 

 each side of the mid-rib, lower with 3 ; stipules herbaceous, 

 persistent ; flowers in a dense, cylindric spike about an inch long 

 on a slightly longer peduncle ; fruits small, dark green, rounded, 

 keeled, with a prominent beak. — Near Ramsey, Huntingdon. 



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