436 ALiSMACE.fi. (WATER-PLANTAIN FAMILY.) 



at the base (l'-4' long, the petiole 4' -12' long); stipules not winged not 

 ridged; peduncle not thickened; fruit obtuse on the back when fresh. (P. lonchltes, 

 Tuckerm.) P. oblongus, Viv., is a small-fruited form. Ponds and slow 

 streams; common. (Eu.) 



12. P. lieterophyllllS, Schreber. Stem slender, branching ; immersed 

 leaves lanceolate or linear and sessile, or only the upper petioled ; floating leaves 

 elliptical, varying to oblong-linear, thinnish (l'-2 ; long), on filiform petioles ; 

 united stipules 2-ribbed on the back ; peduncle often thickened upwards ; fruit slightly 

 keeled when dry (one half smaller than in the preceding). (P. gramineus, L, 

 in part, Fries, $-c. P. Claytonii, Tuckemi.) In shallow pools and ditches, as 

 well as streams ; common. (Eu.) 



P. CRfspus, L., I have not seen in this country. Mr. Tuckerman informs 

 me that he has seen a specimen in a European herbarium, purporting to have 

 been gathered in Delaware. If found, it may be distinguished from No. 8 by 

 its lanceolate and wavy-crisped 3-nerved leaves. See Addend. 



P. DENSUS was admitted into the first edition on the authority of Beck from 

 Schweinitz. I apprehend some mistake about it. The species, if in the coun- 

 try, may be known by its leaves being all opposite and without stipules. 



ORDER 116. AL.ISMACE.#3. (WATER-PLANTAIN FAMILY.; 



Marsh herbs, with scape-like flowering stems, and perfect or monoecious 

 flowers, not on a spadix, furnished with loth calyx and corolla : sepals and 

 petals each 3, distinct. Ovaries 3 -many, distinct or partly so, or if united 

 separating at maturity, forming as many 1 - ^.-seeded pods or achenia. Seed 

 ascending or erect. Embryo without albumen. Stamens hypogynous, 6 

 to many : anthers extrorse, 2-celled. Leaves sheathing at the base. Com- 

 prises two very distinct suborders, viz. : 



SUBORDER I. JUNCAGINE^E. THE ARROW-GRASS FAMILY. 



Calyx and corolla colored alike (greenish). Seed anatropous, with a 

 straight embryo. Leaves petiole-like, without a blade. 



L TRIQLOCIIIN. Flowers perfect. Ovaries 3-6, united into one, but separating in fruit. 

 S. 80IIEUCHZERIA. Flowers perfect. Ovaries 3, nearly distinct, fonuiug diverging pod* In 

 fruit. 



SUBORDER II. ALISMEJE. THE WATER-PLANTAIN FAMILY. 



Calyx green and persistent Corolla white, deciduous. Seed campy- 

 lotropous : embryo bent double or hook-shaped. Leaves commonly rur- 

 nishcd with a blade. 



8. ALTSMA. Flowers perfect, with definite, mostly 6 stamens. Carpels numerous, whorlcct 



4. ECIITNODORUS. Flowers perfect, with 7-21 stamens. Carpels csipitato. ribln-1 



5. SAGITTAKIA. Flowers monoecious. Stamens indefinite. Carpels capitate, winged. 



