386 NAIADACE^. 



4. RLFPPIA. Linn.— Ruppia. 

 (In honor of Henry Bernard Ruppius ; a German botanist.) 



Flowers 2, perfect, naked, on a spadix arising from the sheath- 

 ing base of the leaves. Stamens 2 or 4, sessile. Anthers large, 

 peltate. Ovaries mostly 4. Stigmas sessile, peltate. Fruit 

 drupaceous, pedicellate. 



R. maritima Linn. 



Salt marshes. Can. to Geor. July. %. — Stem long, filiform, branched, 

 floating.. Leaves linear, setaceous, with inflated sheaths. Spadix with 2 naked 

 green flowers, at first very short, but gradually increasing to the length of 5 or 

 6 inches. Anthers large, sessile, bursting horizontally. Drupes olive-green, 

 smooth, crowned with a short oblique beak. Sea Ruppia. 



5. POTAMOGETON. Linn.— Pondweed. 



(From the Greek noranos, a river, and yeiruv, a neighbor ; in reference to ita 

 place of growth.) 



Flowers perfect, on a spadix arising from a spathe. Perianth 

 single, 4-leaved. Anthers 4, nearly sessile, alternating with 

 the divisions of the perianth. Ovaries 4, becoming 4 com- 

 pressed and somewhat cochleate nuts. 



* Upper leaves jloating. 



1. P. natans Linn. : upper leaves floating, coriaceous, on long petioles, 

 oblong-ovate ; lower membranous, linear-lanceolate, gradually tapering 

 into a petiole. P. natans /?. Mich. 



Ponds and lakes. Mass. to Virg. W. to the Platte river. July, Aug. %. — 

 Stem varyinf^in length. Leaves sometimes cordate. Spadix 1^-2 inches long, 

 rising above the water. Broad-leaved Pondweed. 



2. P. fluitans Linn. : upper leaves floating, subcoriaceous, ovate-lan- 

 ceolate, obtuse, tapering into a rather short petiole ; lower very long, lan- 

 ceolate, membranous and sessile. P. natans var. jiidtans Torr. 



Ponds and streams. Can. to Car. W. to the Platte river. July, Aug. %. 

 — Stem xarying in length. Leaves reddish, less coriaceous than in the prece- 

 ding. Spadix an inch long, almost submersed. Floating Pondweed. 



3. P. heterophyllum Schreb. : upper leaves floating, coriaceous, elliptic, 

 petiolate; lower membranous, linear-lanceolate, sessile. P. hybridum 

 Mich. 



Stagnant v^'ater. Can. to Car. Aug. %. — Smaller than the former. In 

 flowing water the leaves are very long and narrow. 



Various-leaved Pondweed. 



4. P. diversifolium Bart. : upper leaves floating, elliptic, petiolate, 5- 

 nerved; lower filiform ; spadix axillary, almost sessile, few-flowered. P. 

 seiaceu7)i Pursh. P. hybridum Torr. 



Ponds and small streams. Can. to Virg. June. %.— Stems numerous, 

 branched, filiform. U]>per leaves scarcely an inch long. Spadix 4 — 6-flowered. 



Small Floating Pondweed. 



