30 MISSOURI BOTANICAL GARDEN, 
convex and slightly keeled above and flat or slightly convex 
to hemisperically gibbous beneath, cavernous throughout, 
cavities very large in the gibbous portion; slightly to 
decidedly unsymmetrical, usually 3-5 nerved; base usually 
acute and commonly with narrow wing margins. Rootcap 
cylindrical, straight or slightly curved, about .25 mm. in 
diameter by 1.3-2.2 mm. long. Spathe irregularly torn 
by the developing flowers; pollen grains globose, spinu- 
lose; pistil clavate, compressed ; stigma concave; style 
long or in the fruit short ; ovules 1-7. Fruit symmetrical, 
purple tinted; seeds with thick covering, prominently and 
unevenly ribbed, with many transverse striations.— Abun- 
dant in ponds. <A cosmopolitan species occurring only in 
the western and southwestern part of our range.— Plate 
2 A. 
This species is reported from the eastern States, but col- 
lections from east of the Mississippi river have failed to 
come under my observation. These are probably the ones 
Austin* refers to his varieties of L. minor. ; 
Specimens examined from Nebraska (Rydberg, no. 1508, 1898); Texas 
(Wright; Mex. Bound. Surv., no. 1411, 1855-56); Wyoming (Forwood, 
1882); New Mexico (Wright, no. 1892, 1852); Arizona (Coues and Pal- 
mer, no. 445, 1865; Toumey, 1894-95); California (Bigelow, 1853-54; 
Brewer, no. 30, 1860-62; Torrey, no. 504, 1865; Kellogg and Harford, no. 
948, 1868-69; Bolander, 1870; Palmer, no. 872, 1875; Cooper, 1879; 
Henney, nos. 104, 106, 109, 112, 1896; Thompson, no. 207, 1896). 
++ ++ Fronds green or purplish beneath, slightly convex, uniformly 
bright green above; fruit not winged; seed always solitary. 
Lemna minor Linn. Sp. Plant. 970. 1753. 
Fronds solitary or few clustered, round to elliptic-obo- 
vate, 1.5-3 mm. wide by 2-4 mm. long; symmetrical, or in 
fruit slightly unsymmetrical; thickish; convex on both 
sides, upper surface sometimes slightly keeled and with a 
row of papules along the midnerve, the apical one usually 
quite prominent; obscurely 3-nerved; cavernous through- 
out. Rootcap comparatively short. Spathe with a small 
* Austin,C, F, Lemnaceae, in A. Gray, Man. Bot. 479. 1867 [5th ed.] 
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