26 MISSOURI BOTANICAL GARDEN. 
2. Unsymmetrical. 
* Obliquely obovate, papulose along the median line. 
+ Convex to strongly gibbous beneath, obscurely 3-7-nerved; 
rootsheath unappendaged. LL gibba. 
+ + Flat beneath, moderately thick, distinctly 3-nerved; root- 
sheath with lateral wing appendages. L. perpusilla. 
* * Long oblong, thin. 
+ Strongly 3-nerved; rootsheath with lateral wing ap- 
pendages. L. perpusilla trinervis. 
+ + Obscurely l-nerved; rootsheath unappendaged. 
L. cyclostasa. 
II. Fronds rootless, with but one reproductive pouch. 
A. Fronds thin, ligulate. WOLFFIELLA. 
a, Saber form; stipe insertion at the lower right-hand angle of the 
two walls of the pouch. 
1, Fronds 14-21 times as long as broad, apex flagellate; stipe scar 
raised. W. Floridana. 
2. Fronds 3-5,5 times as long as broad, apex bluntly rounded; 
stipe scar sessile, rounded. W. oblonga. 
b. Tongue shaped, 1.5-3.5 times as long as broad, large; stipe inser- 
tion on the margin of the lower wall of the pouch. 
W. lingulata. 
B. Fronds thick, more or less globular. WOLFFIA. 
a. More or less flattened above, gibbous beneath, brown punc- 
tate. 
1. Rounded ovate, strongly gibbous, sparingly punctate beneath, 
dorsal surface with a prominent papule near the center. 
W. papulifera. 
2. More or less oblong, less gibbous, abundantly punctate on both 
surfaces, dorsal surface smooth. W. punctata. 
b. Globose to ellipsoidal, not punctate, dorsal surface with usually 
about three inconspicuous papules along the median line. 
W. Columbiana. 
LEMNACEAE. 
Each plant is a fleshy or membranaceous modified stem 
(frond) floating free, beneath or upon the surface of pools 
or slowly running streams. The inflorescence is a very 
simple form of spadix consisting of one pistillate and one 
or two staminate flowers inserted upon a common point. 
The pistillate flower consists of a single carpel containing 
from one to several ovules, and the staminate flower of a 
single stamen. 
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