PONDWEED FAMILY. 65 



Family 3. NAIADACEAE Lindl. Nat. Syst Ed. 2, 366. 1836. 



Immersed aquatic plants with slender, often branching, leaf- the 



leaves flat or filiform, and perfect, monoecious or diocvi.M, Ihry 



or spadiceous flowers. Perianth of 4 segments, or a hyaline envel. ,j v or want- 

 ing. Stamens 1-4 or occasionally more, distinct and hyjx>K.vn<.iis in the per- 

 fect flowers, solitary or connate in the sterile. Anthers extn.r-*-. 1-2 celled 

 Ovaries 1-9, mostly distinct, i -celled, mostly i-ovuled. CarjK-U rarely dehis^ 

 cent. Seeds straight or curved. Endosperm none. 



About 10 genera and 100 species of wide geographic distribution, miwt abundant in trmoente 

 regions. The months noted in the descriptions indicate the fruiting ],. 

 Flowers perfect. 



Perianth of 4 distinct segments. 



Perianth none ; flowers naked. 2 J\'nf>/>ia 



Flowers monoecious or dioecious. 



Leaves entire. 



Leaves i-nerved, I'-j long, X" or less wide. ,//. /////</. 



leaves many-nerved, i~5 long, i"-^" wide. 



Leaves spiny-toothed on the margins, 



i. POTAMOGETON L. Sp. PI. 126. 1753. 



Leaves alternate or the uppermost opposite, often of 2 kinds, submerged and floating, 

 the submerged mostly linear, the floating coriaceous, lanceolate, ovate or oval. Spathe* 

 stipular, often ligulate, free or connate with the base of the leaf or petiole, enclosing the 

 young buds and usually soon perishing after expanding. Peduncles axillary, usually 

 emersed. Flowerssmall, spicate, green or red. Perianth-segments 4, short-clawed (Fig. 154), 

 concave, valvate. Stamens 4, inserted on the claws of the perianth-segments. Anthers 

 sessile. Ovaries 4, sessile, distinct, i-celled, i-ovuled, attenuated into a short erect or 

 recurved style, or with a sessile stigma. Fruit of 4 ovoid or subglobose drupelets, the peri- 

 carp usually thin and hard or spongy. Seeds crustaceous, campylotropous, with an unci- 

 nate embryo thickened at the radicular end. [Greek, in allusion to the aquatic habitat] 



About 65 well-defined species, natives of temperate regions. Besides the following, 3 other* 

 occur in the southern parts of North America. 



Stipules axillary and free from the leaf. 

 With floating and submerged leaves. 

 Submerged leaves bladeless. 



Nutlets more or less pitted. i- /*. nalans. 



Nutlets not pitted. 

 Submerged leaves with a proper blade. 



Submerged leaves of 2 kinds, lanceolate and oval or oblong. 



Uppermost broadly oval or elliptical, lowest lanceolate. ; /'. ampl(Miut. 

 Uppermost lanceolate and pellucid, lowest oblong and opaque. 



4 /' />" 



Submerged leaves all alike, capillary or linear-setaceous, 

 i -nerved or nerveless. 

 3-nerved. 

 Submerged leaves all alike, linear. 



Nearly the same breadth throughout, obtusely pointed, coarsely ceUl 



in the middle. 



Broader at base, acute, without cellular-reticulation. 

 Submerged leaves all alike, lanceolate. 



Uppermost leaves petioled, lowest sessile. 

 All the leaves petioled. 



Floating leaves large, broadly elliptic, rounded or subo 



Floating leaves narrowly elliptical, tapering at base. 7. P. 

 Floating leaves mostly obovate or oblanceolate, tapering al 



All the leaves sessile or subsessile. 



Fruit only i line long, obscurely 3 -keeled. 

 Fruit i X lines long, distinctly 3-keeled. 

 With submerged leaves only. 



Without propagating buds and without glands. 



Leaves with broad blades, mostly lanceolate or ovate, man 



Leaves subsessile or short-petioled, mostly acute < e. ^ ^ 



Leaves semi-amplexicaul, obtuse and cucullate at the apex. 



Leaves meeting around the stem, very obtuse at the apex, not t / uc a . / J/(O 



Leaves with narrow blades, linear or oblong-linear, sevenl-nem-.l 



Leaves oblong-linear, 5 - 7 -nerved, obtuse at the apex. 



Leaves narrowly linear, 3-nerved, acute at the apex. 

 Leaves with narrow blades, capillary or sataceous, i-nerved :>r in^ew 



*Text contributed by the late Rev. THOMAS MORONG. 



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