A REVISION OF THE AMERICAN LEMNACEAE. 33 
Lemna PERPUSILLA Torr. Fl. N. Y. 2: 245. 1843. 
Lemna paucicostata Hglm. ex Engelm. in A. Gray, 
Man. Bot. 681. Jan. 1868. [5th ed. 8th iss. ]|.—Hglm. 
Monogr. Lemnac. 139. May 1868. 
Fronds solitary or more commonly long coherent, form- 
ing groups of 2-6 mature plants; sessile or very short 
stipitate; strongly unsymmetrical, or rarely nearly symme- 
trical in robust sterile individuals; 1.2-2.5 mm. wide by 
2-3.5 mm. long; cavernous throughout. Apical dorsal 
papule usually prominent and frequently a row of smaller 
ones along the midnerve. Wings of the rootsheath varying 
from narrow to broad. Rootcap .85-2 mm. long. Fruit 
unsymmetrical, usually attached obliquely forward and 
outward, ovoid to oblong, ending in a rather prominent 
eccentric style; seed slightly compressed, ovoid to obliquely 
oblong, oblique in the utricle; seed coat thick, ribs promi- 
nent, varying from 12-16 in number, with numerous 
transverse striations. — Common in stagnant ponds through- 
out the eastern portion of our range and extending south- 
ward into South America. Rather variable.— Plate 3 A. 
Dr. Torrey’s original description indicates an anatropous 
ovule, but I have examined type material from his herbarium 
and find the ovule orthotropous, as described in Gray’s 
manual. * 
The original material of Lemna paucicostata Hglm. 
was collected about St. Louis and sent to Hegelmaier 
by Dr. Engelmann. These gentlemen studied the species 
together and in their correspondence referred to it 
as a variety of the Torrey species. In 1868 Engelmann 
published it as a distinct species, giving Hegelmaier the 
credit. This was four months previous to the appearance 
of Hegelmaier’s monograph of the order, and with it his 
own description. I have collected quantities of material 
in the vicinity of St. Louis and identified it with the 
abundant type specimens of paucicostata in the Engelmann 
* Gray, A. Man. Bot. 552. 1889. [6th ed.] 
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