32 24. Zannlchel. 6. FLUVIATILES. Pl.efid.pL 



1. Flowers unisexual ; stamens 1 or 2. 



Fl. on a one-sided spadix ; ovary 1 Zostera. 27. 



FL solitary ; ovaries 2 to 6, sessile, gibbous 



Zannichellia. 24. 



2. FZ. hermaplirodils; stamens^; perigonium 4i-cut. 

 Fl. two-rowed on a solitary spadix ; 



cariopsides 4, on footstalks Ruppia. 25. 



Fl. spiked ; cariopsides 4, sessile .... Potamogiton. 26. 



T. 24. ZANNICHELLIA. Micheli. Pondiueed. 



Flowers solitary, monoicous. — Male. Perigonium none ; 

 stamen 1 ; filament long ; anther 2 or 4-celled. — Fem. Pe- 

 rigonmm campanulate; ovaries 2 to 6 ; stigmata flat, pel- 

 tate; capsule one-seeded, sessile, compressed. — Flowers 

 axillary ; the male at the exterior base of the perigonium 

 of the female flower ; leaves linear, grasslike, 2 or 5 from 

 the same membranaceous sheathing stipula. 



1. ZanjiichelUa palustris. Marsh pondweed. 

 Anthers 4-celled ; stigmata undivided ; capsule keeled, 



toothed at the back. 



Apoiiogeton aqnaticum graminifoliuin, staminibus singiilaribns, Raii 

 Syn. \35. 



Zannichellia paUistris, Lin. S, P. 1375. 

 Horned pon'hveed. 



Ponds and ditches ; annual ; July. 



2. Zannichellia dentata. Toothed po?idweed, 

 Anthers 2-celled; stigmata scolloped; capsule warty. 



Z. paUistris minor, 3Hch. N. G. P.ll. 

 Z. paluslris (3, Lin. S. P. 1375. 

 Z. dt-ntata, Willd. S. P. 



Ponds and ditches ; annual ; July. 



II. 25. RUPPIA. Lin. Gen. PI. Tasselgrass. 



Floivers hermaphrodite, two-rowed on a solitary spadix ; 

 perigonium caducous, 2 valved ; stamens four ; anthers 

 sessile, 2-cclled ; ovaries four, oval, conic ; stigmata obtuse ; 

 nuts four, oneseeded, oval, on a long thi'eadlike peduncle. 

 Plant herbaceous, capillary, branchy; leaves cauline, al- 

 ternate ; //o/aZ leaves mostly opposite; spadix terminal. 



Ruppia maritima. Sea tasselgrass. 



Leaves linear, not nicked at the tip. 



