NAiAS NAIADACEjE 671 



2 Zostera Stems slender, from creeping rootstocks : perianth wanting : 



ovaries and stamens alternate in 2 vertical rows on the inner side of a 

 margined leaf-like enclosed spadix: ovaries pendulous: stigmas 2. 



3 Phyllospadix Stems floating, from creeping rootstocks: flowers dioeci- 



oua, without perianth : anthers sessile, in 2 rows on a spadix : ovaries 

 in 2 rows on the inner side of a margined enclosed spadix, ascending : 

 atigmad 2, linear, sessile. 



i Lilsea Annual stemleps plants: flowers montjecious;8taminate in close 

 spikes on scapes under a single bract; pistillate flowers at the base of 

 the leaves with very long styles, or in dense heads on scapes ; stigmas 

 capitate 



+- -1- Ovaries about 4, nearly sessile, becoming more or less stipitate. 



i KanDichellia Leaves opposite: flowers monoecious, axillary or nearly 

 so : anther solitary, on a slender naked filament : pistillate flowers 

 flolitary,-^th a-cnp^hapeU membranaceous spathe or perianth : stigma 

 peltate. 



6 Buppia Leaves alternate : flowers perfect, 2 or more on an enclosed 

 aptaclix, at length long-exserted, without perianth : anthers 2, sessile : 

 atigma depressed. 



* * Flowers perfect, with herbaceous 4 parted perianth, in a 

 peduncled spike. 



7 Potamogeton Ovaries and anthers 4, sessile : stigma sessile. 



1 NAIAS L. Sp. 1015. 



Slender branching aquatic wholly submerged plants with oppo- 

 site, alternate or verticellate leaves with sheathing bases, and in- 

 conspicuous monoecious or dioecious flowers in axillary clusters or 

 solitary. Staminate flowers of a single stamen and a membranous 

 tubular 4-lobed perianth within a small cup-shaped membranous 

 spathe. Anther 4-celled. nearly sessile : pollen granular Pistil- 

 late flowers without perianth or spathe, the oblong ovary termin- 

 ated by a short style and 3-4 narrowly subulate stigmas. Fruit 

 a membranous utricle, filled by the single erect anatropous seed. 



If flexilis Root. & Pchmidt Fl. Sed. 384. Stem slender, dichotomous- 

 ly much branched 6-18 inches long: leaves linear, acuminate or abruptly 

 acute, 6-12 lines long. >^-l line wide, numerous and crowded upon the up- 

 per part of the branches, with 25-30 minute teeth on each side; sheaths 

 obliquely rounded, with 5-10 teeth on each margin : fruit ellipsoid, with 

 very thin pericarp, 1-2 lines long: style long, persistent; stigmas short : 

 seed smooth, shining, straw-color, sculptured with 30-40 rows of nearly 

 square or hexagonal reticulations. In ponds and streams, throughout 

 nearly all parts of North America: also in Europe. 



N. Gaadalupensis Morong Mem. Torr. Bot. Club, iii, 60. Stem near- 

 ly capillary 1-2 feet long, widely branched from the base : leaves numerous . 

 6-9 hues long, J^-J^ line wide, acute, opposite or in fascicles of 2-5, fre- 

 quently, recurved, with 40-50 teeth on each margin: fruit about a line long; 

 pericarp dark and strongly marked by 15-20 rows of hexagonal or rectangu- 

 lar reticulations which are transversely oblong: seed straw-color, not 

 shining. , In ponds and streams, Oregon to Nebraska and Texas : also in 

 tropical America. 



2 ZOSTERA L. Sp. 968. 

 Marine plants with creeping rootstocks, branching compressed 



