A GUIDE AND KEY TO AQUATIC PLANTS 103 



3. Peltandra Raf. 



1. Spathe narrow, green throughout; fruits green 1. P. virginica. 



1. Spathe broad and spreading, mostly white; fruits 2. P. glauca. 

 crimson. 



1. P. virginica (L.) Kunth Arrow-arum — Well distributed in 

 swamps and shallow water over all of our territory, frequent. 



2. P. glauca (Ell.) Feay. Wliite Arrow-arum— Very acid swamps 

 or ponds, Coastal Plain, Florida to Alabama and North Carolina. 

 Not nearly as frequent as the preceding. 



4. Pistia L. 



P. stratiotes L. Water-Lettuce — Floating plant very often forming 

 a complete carpet oa streams, lakes and ponds in the Coastal Plain in 

 Florida. Found westward to Louisiana and may be present in Ala- 

 bama and Mississippi. It is very often in association with species of 

 Mansonia. 



LEMNACEAE Duckweed family 



1. Wolffia Horkel 



1 . Plant rounded on back ; not covered with minute brown 



dots. 1- W. Columbiana. 



1. Plant flat on back ; covered with minute brown dots 2. W. punctata. 



1. W. Columbiana Karst. Watermeal — Smallest, with the next, of 

 our flowering plants. When abundant, they form a granular layer on 

 the surface of ponds or lakes. Both this and the following species are 

 well distributed over our territory. 



2. W. punctata Griseb. Watermeal^ All that has been said of the 

 preceding applies to this species except that it has not been as fre- 

 quently noted. These two species are listed under Bruneria by Small. 



2. Wolffiella Hegel 



W.jioridana (J. D. Smith) C. H. Thompson. Bog-mat — Very com- 

 mon, even in very acid waters, in the Coastal Plain of our territory. 

 It has been taken as far north as Reelfoot Lake, Tennessee, in the 

 Mississippi Valley. 



3. Lemna L. 



1. Joints or disks long, narrow and stalked; plants com- 1. L. trisulca. 



monly forming masses below surface of water. 



1. Joints not stalked; floating on surface of water 2. 



2. Joints symmetrical or nearly so 3. 



2. Joints asymmetrical 4. 



3. Joints elliptic-obovate 2-4 ram. long; fruit lenticular 2. L. minor. 



3. Joints elliptic or oblong 1.5-3.9 mm. long; fruit elongate. 3. L. minima. 



