Zannichellia. NAJADACE^. 253 



1. Zannichellia palustris, Linn. Horned Pondweed. 



Linn. sp. 2. p. 969 ; Engl. hot. t. 1844 : Pursh, fl. 1. p. 4 ; MuU. cat. p. 86 ; Torr. 

 compend. p. 330 ; Beck, hot. p. 384 ; Hook.Jl. Bor.-Am. 2. p. 170 ; Kunth, enum. 3. p. 124. 

 Z. intermedia, Torr. I. c. ; Beck, I. c. 



Annual. Stem submerged, filiform, much branched. Leaves 1-2 inches long, extremely 

 narrow, entire. Flowers monoecious, usually both kinds from one axil. Stamen longer than 

 the pistils ; the filament slender : anthers large, 2-celled ; the connective produced beyond 

 the cells into a short point. Ovaries usually 4, but sometimes 2, 3 or 5, arising from a 

 membranaceous cupshaped involucre, which is 2-lobed at the orifice : stigmas excentrically 

 peltate, obliquely inserted on the style, repandly toothed or entire. Fruit a little incurved ; 

 the sides compressed, mostly entire, but sometimes a little toothed on the back ; the persis- 

 tent style or beak variable in length, sometimes as long as the fruit, at other times much 

 shorter : epicarp membranaceous : endocarp coriaceo-crustaceous, thin. Seed oblong, cy- 

 lindrical : integument simple, membranaceous. Embryo with the radicular extremity inferior 

 and somewhat bulbous ; the upper extremity (cotyledonous) tapering to a long point, and 

 circinately involute. 



Ponds and slow-flowing waters, often in those which are brackish. Staten Island, «&c. Near 

 Penn-Yan {Dr. Sartwell). Lake Champlain {Mr. Oakes). Fl. July - August. 



5. POTAMOGETON. Linn. ; Endl. gen. 1564.. pondweed. 



[From the Greek words potamos, a river, and geiton, a neighbor ; in allusion to its place of growth.] 



Flowers perfect. Perianth 4-leaved ; the aestivation valvate. Sepals unguiculate. Stamens 

 4 : filaments short : anthers 2-celled, opening longitudinally. Pistils 4, sessile, convex on 

 the back : style short or none : stigma simple : ovule ascending. Nucules 4, compressed, 

 tricarinate ; the shell coriaceous or ligneous. Seed curved, with a thin testa. — Aquatic 

 herbs ; the leaves submerged, or the upper ones floating, distichous, alternate or rarely 

 opposite, membranaceous. Flowers in pedunculate axillary or terminal spikes. 



§ 1. Stipules connate, free from the petiole. 

 * Upper leaves floating, broader than the suirmersed ones. 



1. PoTAMOGETON NATANS, Linn. Broad-lcaved Floating Pondweed. 



Stem simple ; leaves on long petioles, many-nerved ; the floating ones (large) ovate or 



oblong, coriaceous, obtuse or somewhat cordate at the base ; the submersed ones linear or 



lanceolate, membranaceous (often wanting) ; fruit keeled. — Linn. sp. 1. p. 126 ; Engl. hot. 



t. 1822 ; Michx. fl. 1. p. 101 ; Pursh, fl. 1. p. 120 ; Bigel. fl. Bost. p. 63 ; Torr. ft. 1. 



