534 NAiADACEiE. [Potaniogetoii. 



Order LXXXV. NAIADACE^, Juss. 



" Flowers perfect and all sessile, or imperfect and monoecious or 

 dioecious. Perianth ? of the perfect flowers of 3 — 4 wedge-shaped 

 or clawed scales, or wanting ; of the imperfect ones usually want- 

 ing, sometimes of 1 — 2 scales. Stamens definite, hypogynous. 

 Ovaries solitary or several, 1-celled. Ovules usually solitary, erect 

 or pendulous, rarely 3 and erect. Style simple, or more or less 

 deeply 2 — 3 cleft. Pericarps dry, indehiscent, 1-celled, 1- (or 

 rarely 2-) seeded. Embryo without albumen, with a thin skin, 

 having a lateral cleft for the emission of the plumule. Radicle 

 next the hilum, or at the opposite extremity of the seed. — Sub- 

 merged or floating aquatics ivith very cellular leaves and stems. 

 Flowers inconspicuous, sometimes spiked." — Br. Fl. 



I. PoTAMOGETON, Linn. Pondweed. 



" Flowers perfect, sessile, ujion a spike (or spadix ?) which issues 

 from a sheathing hractea (or spatlia?). Perianth single, of 4 

 clawed scales. Stamens 4. Anthers sessile, opposite the scales 

 of the perianth. Pistils 4, which become 4 sessile achenes. 

 Styles and stigmas undivided." — Br. Fl. 



* Leaves alternate, upper ones floating , broader than the rest. Stipules free. 



1. P. natans, L. Broad-leaved Pondiveed. " Lower leaves 

 linear submembranaceous or wanting, upper elliptical coriaceous 

 floating on long stalks manj^-nerved distinctly cellular, fruit (large) 

 keeled at the back."— 5r. Fl. p. 471. E. B. t. 1832. 



In ponds, ditches and slow streams; frequent, i^/. June, July. If. 



2. v. ohlongus, Vir. Oblong-leaved Pondiveed. "Leaves all 

 stalked, upjjer ones coriaceous floating oblong-elliptical, lower 

 linear-lanceolate, achenes minute with their back alwaj's obtuse 

 and rounded, spike slender cylindrical densely flowered upon a 

 long terete peduncle." —B«fc. E. B. S. t. 2849. Br. Fl. p. 470. 

 P. natans £., Mert. and Koch. 



In wet ditches and bogs, on marshy heaths, &c. ; I believe a very common spe- 

 cies with us. FL July. If. 



E. Med. — On Blackpan and Lake commons. 

 W. ilfed.— Cockleton bog ? 



** Leaves alternate, ovato-lanceolate or oblong, all submersed. Stipules free. 



3. P. lucens, L. Shining Pondvjced. " Leaves stalked elliptic- 

 lanceolate mucronate denticulate flat, with several opposite pairs 

 of parallel nerves springing from the midrib connected by reticu- 

 lations, stipules winged, spikes cylindrical many-flowered." — Br. 

 Fl. p. 468. E. B. t. 376. 



