322 ORDER 134 ALISMACE^E. 



/3. dicer ifbUus Leaves nearly all floating, oval, the lower few and short. 



4 P. Spirillus Tuckm. Very delicate, branched ; floating Ivs. oval to lanceolate, 5-9 



veined, 7 10", on short broad petioles ; lower leaves narrowly linear, obtuse, 12 , 

 submersed ped. 1-2-flowered ; embryo a little spiral. Streams : rare. 



5 P. gramineus L. Stem much branched, terete; floating Ivs. long-stalked, ovate 



to oblong, acutish, 13-veined ; lower leaves lanceolate to lance-linear, pointed, stip. 

 obtuse ; fruit small, obtuse-angled. Common, and very variable. 



6 P. fl ultaiis Roth. Lvs. long-stalked, the floating thinnish, opposite, elliptic-oblong, 



the submersed linear-oblong, all acute both ways, 11-21-veined ; fruit acutely 3-keeled 

 on the back. In ponds and rivers. (P. lonchitis Tuckm.) 



7 P. pulclier Tuckm. Stem simple ; floating leaves ovate, subcordate, 25-35-veined, 



o-5', alternate; upper submersed Ivs. lanceolate, long-acuminate, undulate, the lower 

 oval-oblong ; fruit 3-keeled. Penn., N. J. (Prof. Porter), N. and W. Rare. 



8 P. amplifollus Tuckm. Stems simple ; floating leaves oval to elliptical, 2f 4', 



35-45-veined, on long, opposite stalks ; submersed Ivs. larger than the floating, 57', 

 lanceolate, short-stalked, or sessile. Ponds. (P. fluitans C-B.) 



9 P. lucens L. Leaves large, often shining, iance-oval, 3 5' x V, pointed and mucro- 



nate, on short stalks ; spike 2' ; fruit roundish, slightly keeled. Rivers and lakes. 



10 P. obrutus Wood. Stem simple: leaves all submersed, narrow-lanceolate, 3', ob 

 scurely 7-veined, subsessile, acute ; spike 1', the stalk 2' ; fruit inflated, acutely keeled, 

 conspicuously umbilicate both sides. Slow waters. No floating leaves. 



1 1 P. praelongus Wulf. St. very long, branched ; Ivs. lance-ovate to lanceolate, ob- 

 tuse, half-clasping, often large ; peduncle very long (3 5') ; fruit sharp-keeled. Rivers. 



12 P. perfoliatus L. Stem branched ; Ivs. cordate-clasping, roundish to ovate, ob- 

 tuse ; ped. short, few-flowered ; fruit not keeled. Ponds and slow waters : common. 



13 P. crispus L. Branched below; leaves 3-veined, half-clasping, narrow-oblong, 

 obtuse, 12'. cri^p-wavy ; fruit acuminate-beaked. Penn., and E. (Prof. Porter). 



14 P. pectinatus L. Stem flexuous, repeatedly forking; leaves linear-setaceous, 

 23' ; spike interrupted, on a long filiform peduncle ; fruit large (2 r/ ), rough. E. and N. 



15 P. Kofobinsii Oakes. Stem very branching ; leaves lance-linear, crowded, sheath- 

 ing the stem with their bases ; spikes on short peduncles. N. and W. 



1 6 P. compressus L. St. branching, flattened ; Ivs. linear, OO-veined, 24' x 12" ; 

 stip. obtuse ; spike 12-15-flowered, much shorter than the peduncle. Ponds. 



1 7 P. obtusiiolius Mert. and Ktch. St. branching, flattened ; Ivs. linear, 3-veined ; 

 stip. obtuse ; spike 6-8-flowered, as long as the peduncle. Pa., and N-W. 



18 P. pauciflorus Ph. St. slightly flattened, much forked ; Ivs. linear, 1 3"xJ 1"; 

 flowers few (312) in the spike ; fruit distinctly ccested. Rivers, &c. 



19 P. pusillus L. Stem filiform, branched ; leaves linear, varying to capillary, 1- 3- 

 veined ; spikes 3-5-flowered, long-stalked ; fruit not keeled. Shallow waters. 



20 P. Tucfcermani Robbing. Very slender and delicate, forked ; Ivs. capillary and 

 confervoid ; spike 6-9-flowered, on a very long peduncle (5'). Ponds, Pa., and N. 



COHORT 6. FLOKIDE^E. 



ENDOGENOUS PLANTS with the flowers usually perfect and 

 complete, the perianth double, 3-parted, the outer often, and 

 sometimes both, green. 



ORDER CXXXIV. ALISMACEJE. WATER PLANTAINS. 



Marsh Tierbs, with parallel-veined, petiolate leaves and branching pedun- 

 cles. Flowers perfect or monoecious, with a regular double perianth, 



