70 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
forms have until recently been supposed to represent the specific differentiation of the 
American members of the group. Their number is now increased to nineteen. 
KEY TO THE AMERICAN SPECIES. 
Width of leaf blade less than half the length; sinus less 
than one-fourth the length of the blade. 
Sinus usually closed; length of blade 2.5 times the 
breadth or less; fruit about 2 cm. long; seeds 
3 mm. long; stigma rays elliptical; leaves 
acutish.........2.. 222.0022 2 eee eee eee ll. N. ulvacea. 
Sinus usually open; length of blade over 3 times the 
breadth; fruit about 3 cm. long; seeds 4 mm. 
long; stigma rays linear; leavesobtuse....... 10. . sagittifolia. 
Width of leaf more than one-half its length; sinus one- 
half to one-fourth the length of the blade. 
Calyx of more than 6, usually 9, parts............... 17. N. polysepala. 
Calyx of usually 6 parts. 
’ Petioles conspicuously flattened; leaves floating. 
Anthers shorter than the filaments. 
Stigma rays less than 10; flowers less 
than 20 mm. in diameter; sepals 
NAITOW. . 2.2... eee eee eee eee eee 1. N. microphylla. 
Stigma rays more than 10; flowers 
about 30 mm. in diameter; sepals 
broad. 22... 2..2.-22.-2222-025- 2. N. rubrodisca. 
Anthers at least equaling the filaments. 
Capsules about 40 mm. high and 30 mm. 
in diameter; flowers about 45 
mm. in diameter; leaves broadly 
rounded. .........2.-.----2----- 3. N. americana. 
Capsules about 25 mm. high and 18 
mm. in diameter; flowers 22 to 
26 mm. in diameter; leaves 
acutish......22.2...0.2.2222.-- 4. N. fraterna. 
Petioles subterete; leaves erect or floating. 
Lower surface of leaves glabrous. 
Leaves ofan orbicular type............ 8. N. fluviatilis. 
Leaves conspicuously longer than broad. 
Submersed leaves present; leaves 
and sepals very thin... .... 9. N. chartacea. 
Submersed leaves wanting; leaves 
and sepals thick. 
Sinus closed; stigma rays 
usually more or less con- 
fluent at the base, 
broad; disk usually 
oval... .....2....... 7. N. ludoviciana. 
Sinus usually open; stigma 
rays not confluent at 
the base, narrower; disk 
orbicular, 
