NAIADACEiE. (PONDWEED FAMILY.) 469 



1. NAIAS, L. 



Flowers monoecious or dioecious, axillary, sessile, destitute of calyx aud 

 corolla, yterile flower monandrous, enclosed iu a spathe. Anther 4-celled, 

 opening at the apex, the filament lengthening. Fertile flower naked ; the 

 sessile ovary pointed with the slender style. Stigmas 2-4, subulate. Ovule 

 erect. Acheniura minute. Embryo straight. Radicle inferior. — Stems fili- 

 form, forking. Leaves opposite or whorled, linear, dilated into a short sheath 

 at the base. Flowers solitary, minute. 



1. IT. flexilis, Rostk. Stem immersed (l°-2° long); leaves 3 in a 

 whorl, narrow-linear, membranaceous, spreading, minutely denticulate on the 

 margins, the lower ones often remote ; stigmas 3 - 4 ; achenium elliptical, 

 acute, smooth, yellowish. — In pouds and still water, South Carolina, aud 

 northward. July - August. — Leaves about 1' long. 



2. N. miorodon, A. Braun. Stem (6'- 12' long) almost capillary, very 

 leafy throughout; leaves opposite, approximate, spreading or recurved (2"- 

 4" long) ; aclienium narrowly spindle-shaped, finely reticulated, brownish. — 

 Fresh or brackish water along the coast. West Florida. July -August. 



3. N. maj or, All. Stem muricate ; leaves broadly linear, serrate-dentate, 

 with muricate teeth, the sheaths entire ; flowers dioecious ; anthers 4-valved ; 

 style very short ; stigmas 3 ; achenium elliptical, obscurely reticulate. — South 

 Florida. 



2. ZOSTERA. L. Eel-grass. 



Flowers monoecious, naked ; the sterile and fertile ones alternately arranged 

 on the anterior edge of a flattened membranaceous spadix, and enclosed in 

 the sheath-like base of the leaves. Anthers oblong, 1-celled, filled with fine 

 filaments instead of pollen grains. Ovary fixed near the apex, containing a 

 single pendulous orthotropous ovule, and pointed with the subulate persistent 

 style. Stigmas 2, capillary. Utricle bursting irregularly. Seeds striate. 

 Cotyledons inflexed-curved, received in a longitudinal cleft of the embryo. — 

 Marine herbs, with creeping stems, and narrowly linear obtuse and elongated 

 sheathing leaves. 



1. Z. marina, L. Stem slender, terete, jointed ; leaves thin and tender, 

 faintly 3 - .5-nerved ; flowers in two rows on the linear spadix. — Deep salt- 

 water coves. West Florida, and northward. August -Sept. 



3. ZANNICHELLIA, L. 



Flowers monoecious, axillary. Sterile flower consisting of a solitary naked 

 filament hearing a 2 - 4-celled anther. Fertile flower from the same axil, com- 

 posed of 2 - 6 sessile 1-celled ovaries, surrounded by a cup-shaped involucre, 

 and pointed with the slender style. Stigma obliquely peltate. Ovule sus- 

 pended, orthotropous. Achenium oblong, stalked. Embryo slender, coiled. 

 — Submerged aquatic plants, with filiform branching stems, and very narrow 

 and entire alternate leaves, with sheathing stipules. 



1. Z. palustris, L. Stems tufted; leaves acute, l-ne^^'ed; anther 2- 

 celled; achenia 3-6 in a cluster, linear-oblong, commonly short-peduncled. — 

 Fresh or brackish water, Florida, and northward. May -August. — Stems 

 l°-3° long. Leaves \'-2' long. 



