THE LIGULATE WOLFFIAS OF THE UNITED STATES. 
BY CHARLES HENRY THOMPSON. 
Of the Lemnaceae, represented in our flora by Lemna, 
Spirodela, and Wolffia, the Wolffias present two very 
marked forms designated by Hegelmaier as subgenera — 
Euwolfia and Wolfiella.* In our species these are char- 
acterized by small granular symmetrical fronds for the first, 
and comparatively large, thin, strap-like unsymmetrical 
fronds for the latter. Huwolfia is represented by two 
species, both of which are known to be fertile. Wolffella, 
however, has never been known to produce flowers. 
Though there is no doubt that it belongs to this order, 
yet there is a question whether it is properly a Wolffa. 
My observations lead me to consider Wolffiella a good 
genus, as has been suggested,t with structural characters 
intermediate between the Wolffias proper and the Lemnas, 
but this distinction could hardly be recognized as conclu- 
sively generic without the support of generic differences 
in their flowers, which latter it is hoped will yet be dis- 
covered as their habitats are. more thoroughly explored. 
This subgenus has heretofore been reported as having but 
one representative in the United States,and that a variety 
of a Mexican species, growing in the subtropical region of 
Florida. 
Since this variety and another Mexican species have both 
only recently come under my notice—both from new 
localities with us —it seems fitting that a careful report 
be made on them from the facts which I have been enabled 
* Hegelmaier: Die Lemnaceen, pp. 122, 131. 
+ J.D. Smith: Bull. Torr. Bot. Club, vir. 65. 
(101) 
