Part 1, 1909] ZANNICHELLIACEAE 
Floating leaf-blades more than 3.4 cm. long; submerged leaves 
with cellular reticulation along the midrib. 
B. Mature submerged leaves lanceolate, ovate or elliptic, never linear or 
less than 4 mm. wide except in forms of P, heterophyllus. 
Keels of the fruit dentate or tuberculate. 8. 
Keels of the fruit, if any, smooth. 
Floating leaves 32-many-nerved. 9. 
Floating leaves fewer-nerved. 
Submerged leaves mostly 7-nerved, at least the lowest sessile. 
Submerged leaves serrulate at apex. 10. 
Submerged leaves entire. 
Plant green ; submerged leaves narrower than the floating. 11. 
Plant red; submerged leaves as wide as or wider than the 
floating. 12. 
Submerged leaves more than 7-nerved, all petiolate. 
Floating leaf-bases merely rounded or acute, not cordate; 
submerged leaves as wide or nearly as wide as the 
floating. . 
Floating leaves elliptic-lanceolate, the apex acute or obtuse, 
not mucronate. 
Floating leaves not spatulate. 
Floating leaves rounded at base, the primary nerves 
mostly more than 5. 
Floating leaves acutely narrowed at base, the primary 
nerves mostly 5. 
Floating leaves spatulate. 
Floating leaves ovate, mucronate. 
Floating leaf-bases cordate or subcordate. 
Nutlets prominently 3-keeled ; style 1.5 mm. long. 
Nutlets inconspicuously 1-keeled; style almost wanting. 
2. With submerged leaves only. 
A. Leaves of a lanceolate, ovate, or orbicular type, never linear. 
Leaves stalked or merely sessile, not perfoliate. 
Without propagating buds, the elliptic-ovate leaves serrulate only 
P: 
2: 
aes 
P. 
15 
P. epthydrus, 
mexicanus. 
amplifolius. 
angustifolius. 
. heterophyllus, 
alpinus. 
americanus. 
occidentalis. 
Faxont. 
tllinoensts. 
. PB. pulcher. 
. P. polygonifolius, 
at apex. . BP. lucens. 
With propagating buds, the oblong-lanceolate leaves serrulate 
throughout. 20. P. crispus. 
Leaves perfoliate. 
Leaves cucullate ; the straight apex of the embryo pointing towards 
the base. 2 
Leaves not cucullate ; the curved apex of the embryo pointing inside 
the base. 
B. Leaves all linear. 
Stipules adnate to the leaf-bases. 
Leaves at least 1 mm. wide, with an acute, acuminate or obtuse tip. 
Nutlets inconspicuously 1-keeled or without keels. 
Leaves 3-nerved, 2 mm. wide or more. 
Leaves 1-nerved, less than 1.5mm. wide. 
Nutlets 3-keeled. 
Leaves serrulate ; inflorescence branched. 
Leaves entire ; inflorescence not branched. 
Leaves capillary, less than 0.5 mm. wide. : 
Nutlets 2.5 mm. long or more, style at least 0.5 mm. long. 
Nutlets 2mm. long or less; style almost wanting. 
Sheaths of stipules less than 6 mm. long. 
Sheaths of stipules more than 1 cm. long. 
Stipules free from the leaf-bases. 
Leaves at least 1.6 mm. wide. 
The straight apex of the embryo pointing towards the base. 
Keels of the fruit crested. 
Keels of the fruit smooth. 
The curved apex of the embryo pointing inside the base. 
Keels of the fruit undulate or toothed. 
Without propagating buds; leaves 3-nerved. 
With propagating buds; leaves many-nerved. 
Keels of the fruit smooth. 
Leaves all capillary, less than 0.9 mm. wide. 
Nutlets without keels or obscurely keeled. 
Plant without propagating buds, the straight apex of the em- 
bryo pointing outside the base. 
Plant with propagating buds, the curved apex of the embryo 
pointing inside the base. ae . 
Nutlets keeled, or at least with 2 grooves culminating in 3 
ridge-like keels. 
The straight apex of the embryo pointing towards or outside 
the base. Paes 
The curved apex of the embryo pointing inside the base. 
Without propagating buds; keels of fruit dentate orcrisped. 36. 
With propagating buds; keels of fruit, if any, smooth. 34. 
23. 
28. 
24. 
25. 
1. P. praelongus. 
22. P. perfoliatus. 
P. latifolius. 
P. interior, 
P. Robbinsit. 
£. interruptus. 
. P. pectinatus, 
. BP. filtformis, 
. P. interior, 
. PB. foliosus, 
. PB. Friestt, 
. PL. Hillit. 
. PB. compressus. 
. P. obtustfolius, 
33. P. rutilus. 
34. P. pustlius. 
35. P. foliosus. 
P. confervoides. 
P, pusillus, 
