(spadderdock), Nymphoides aquatica (Gmel.) O.Ktze and Brasenia 

 shreberi Gmelin. A second group of floating -leaved taxa are 

 unrooted in sediments and free-floating. These taxa, which include 

 Lemna minor L. (duckweed), Pistia stratiotes L. (water-lettuce) and 

 Salvinia rotundifolia Willd., obtain their nutrients from the water and 

 exhibit adaptations that keep the plant afloat. Eichhornia crassipes 

 (Mart.) Solms. is a floating-leaved species introduced to Florida, 

 which because of its rapid spread and prolific growth, has become a 

 severe economic and environmental problem (Tarver et al. 1979). 



Emergent taxa, which grow erect in shallow aquatic areas and do 

 not depend on the water for support, demonstrate the third growth 

 form in macrophytes. Common examples of these taxa are Typha 

 spp. (cattails), which was the macrophyte with the most extensive 

 areal coverage in a large survey of Florida lakes (Schardt 1983), and 

 Sagittaria latifolia Willd. 



Some taxa exhibit growth patterns that are typical of more than 

 one growth-form category. Hydrocotyl umbellata L., for instance, 

 grows mostly as a submerged plant though leaves are frequently 

 emergent in shallow water. Portions of Hydrocotyl mats occasionally 

 break away and are redistributed as floating vegetation. 

 Potamogeton spp. also exhibits extensive lateral submerged growth, 

 but bears some floating leaves at the surface. 



Environmental Factors Influencing Macrophyte Distribution 

 Many studies have been conducted to determine which 

 environmental factors most affect the distribution and abundance of 

 macrophytes, and many of these studies have come to different 



