16 ZANNICHELLIACEAE 
regions.—POoNDWEEDS.  FisHWEEDS.—Both the submerged ane the floating 
inds often occur in such dense masses that navigation by small boats is 
seriously im mpeded. Plants are sometimes collected en masse and oe as fer- 
tilizer. Our plants usually flower in sum. 
Stipules axillary, free from the lea 
Plant P DOE submerged E D leaves. 
Submerged leaves without blades. 
loeng leaves with ovate or oval er oe eee or rounded at the 
base: flowering spikes , 0-0 m 
thic . P. natans. 
Floating leaves with narrowly elliptic Dee acute 
at both C flowering spikes 1-2 . long, 
| 2,5-4 mm. 2. P. floridanus. 
Subme rged EF with normal blades. 
Blades of submerged leaves of 2 form 
Blade of the floating leaves Coro dte at the 
base: druplet- beak erect. 3. P. pulcher. 
Blade of the floating leav A rounded at the 
base: deupelet heal obliqu 
Blades of submerged Jeaves fes bike. 4. P. amplifolius. 
Submerged leaves with ear or nearly linear 
blades. l 
Leaf-blades with coarsè cellular reticulation 
in the middle. 5. P. epihydrus. 
Leaf- blades with inconspicuous cellular 
reticulation 6. P. heterophyllus. 
es te ed es ‘with lanceolate or oblanceo- 
ate bl 
Leaf. blades disti netly petioled. 7. P. fluitans. 
8. P. angustifolius. 
Leaíf- Dc sessile or nearly so. 
Plant with subm s only. 
Leaf-blades bro 
Blade EROR petioled oe nearly sessile. 9. P. lucens. 
10. P. perfoliatus. 
11. P. Curtissii. 
Blade clasping the st 
Leaf- EXE ins or filiform. 
e 1- 'e 
Blade 3-nerved. 
I crested : plants without propagating 
or glan nds. 12. P. foliosus. 
Drupelet crestless : plants with both propa- . 
ating buds and glands. 13. P. pusillus. 
Stipules sans a ~ blades or to the petioles of the sub- 
ged leave 
Plant a vith both "submerged and floating leaves: drupelet 
creste 14. P. diversifolius. 
Plant with submerged leaves only: drupelet crestless. 15. P. pectinatus. 
1. P. natans L. Leaves of 2 kinds, the submerged phyllodia, the floating 
ones with ovate or oval blades 4-9 em. "long, rounded.or subcordate at the base: 
anther notched at the apex: drupelet sho: 
void, 4—4.5 mm. long, scarcely keeled.— 
aes water and slow streams, various prov- 
inces, s to Calif., B. C, and N. S.— 
(Eurasia. ) 
2. P. floridanus Small Smaller than P. 
natans: floating leaves with narrowly ellip- 
tie blades 4—7 em. long, acute at both ends: 
anther apiculate at the apex: drupelet 
smaller than in P. natans.—Blackwater 
River, W Fla 
3. P. pulcher oe Leaves of 3 kinds, 
he lower in LL ed ones leathery, the 
blades spat ovate, the upper submerged ones narrower, flimsy, 
floating pum "ith leathery ovate or DUAE -ovate, cordate blades: qe 
