Hi NAIADACES. (POND WEED FAMILY.) 



Order 138. NAIADACE7E. (Pondweed Family.) 



Aquatic herbs, with slimier jointed leafy immersed stems, and perfect 

 monoecious or dioecious flowers, destitute of floral envelopes, or with 

 Bcale-like Bepals. Stamens 1-4: anthers 1-4-oelled. Ovary 1-celled, 

 forming a 1-seeded, aeheniiun in fruit. Stigmas 1-4. Seed without al- 

 bumen. Embryo straight, curved, or coiled. — Leaves sheathing, or with 

 sheathing stipules. Flowers commonly enclosed in a spathe. 



Synopsis. 



* Flowvrs monoecious or dioecious. 



1. NAIAS. Stigmas 2-4. Flowers naked. Leaves opposite or whorled. 



2. Z< >sTERA. Stigmas 2. Flowers enclosed in a spathe. leaves alternate. 



;;. /.ANNH'HELLIA. Stigma single, peltate. Ovaries 4, from a cup-like involucre. 

 » * Flowers perfect. 



4. RTTFPTA. Fruit long-peduncled, umbellate. Calyx and corolla none. 



5. POTAMOGETON. Fruit sessile, spiked. Calyx 4-kavcl. 



1. NAIAS, L. 



Flowers monoecious or dioecious, axillary, sessile, destitute of calyx and co- 

 rolla. Sterile flower monandrous, enclosed in :i spathe. Anther 4-celled, open- 

 ing at the apex, the filament lengthening. Fertile flower naked ; the sessile 

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

 Acheninm minute. Embryo straight. Radicle inferior. — Stems filiform, fork- 

 ing. Leaves opposite or whorled, linear, dilated into a short sheath at the base 

 Flowers solitary, minute. 



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

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



the lower ones often remote; stigmas .'5 - 4 ; aehenitnn elliptical-, acute, smooth, 

 yellowish. (Caulinia tlexilis. Wffld.) — In ponds and still water, South Caro- 

 lina, and northward. July and Au<r. — Leaves about 1' long. 



Var. ? fusiformis. Stem (6' -12' lonp) almost capillary, very leafy 

 throughout ; leaves opposite, approximate, spreading or recurved (2"-4" long) : 



achenium narrowly spindle-shaped, finely reticulated, brownish. — Brackish 



water along the coast West Florida. July and Aug. 



2. ZOSTERA, L. Ebl-gbass. 



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

 on the anterior edge of a Battened membranaceous Bpadix, and enclosed in the 

 Bhcath-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 pen- 

 dulous orthotropous ovule, and pointed with the subulate persistent Btyle. Stig- 

 mas 2, capillary. Utricle bursting Irregularly, Seeds Btriate. Cotyledons in- 

 fiexed-curved, received in a longitudinal cleft of the embryo — Marine herb-, 



with creeping stem-, and narrowly linear ObtUM and elongated shcathm- i 



