Aquatic Veg^etation and Control Measures 169 



artificially introducing a variety of submersed and emergent aquatic plants 

 into a newly-impounded water area. Usually only a few kinds will survive 

 and these are the species that might be expected to move in naturally. 

 Experience has shown that it is often a complete waste of money to 

 purchase aquatic vegetation for plantings in new impoundments, par- 

 ticularly if these species are not common in similar waters. 



Types of Aquatic Plants 



Aquatic vegetation exclusive of bacteria may be separated into several 

 types : 



Algae 



(1) Plankton algae— free floating cells of single or colonial habit, forming 

 characteristic groups, plates, short strands, or spheres with or without 

 power of movement: Phacus, Scenedesmus, Microcystis, Pandorina. 



(2) Filamentous algae— usually forming strands or threads of cells which 

 may grow on the pond bottom but often float to the surface forming 

 scums or floating mats of hairlike strands: Spirogyra, Zygnema. 



(3) Algae that grow upward from the pond bottom in a plant form not 

 unlike that of some of the higher plants: Nitella, Chara. 



Higher Plants 



(4) Floating aquatic plants— unattached and floating about on the surface: 

 Water hyacinth (Echhornia), Watermeal (Wolffia) , Duckweed 

 (Lejnna). 



(5) Submersed aquatic plants— mostly below the surface and supported 

 by the water: Pondweeds {Potamogeton) , Coontail {Ceratophyllum) , 

 Waterweed (Elodea) , Milfoil (Myriophylhnn) . 



(6) Emergent aquatic plants— mostly above the surface and self-support- 

 ing: Cattails (Typha), Buhush (Scirpus), Arrowheads (Sagittaria) , 

 Figure 6.11. 



(7) Woody plants and trees— not true aquatics but usually associated with 

 water: Button bush (Cephalanthus) , Cypress (Taxodiuin) , Willows 

 (Salix). 



These plants serve the same functions in an acpatic habitat as in a 

 terrestrial one, i.e., some are sources of food for herbivorous animals, some 

 represent substrata upon which certain animals live, still others serve as 

 cover and a mechanical aid in escape from natural predators. 



Aquatic plants compete for space in an aquatic environment much 

 as terrestrial plants do. However, the environment of the former is less 

 stable than the terrestrial environment, and for this reason the plant 

 communities are much less stable. This is particularly true of the algae 

 which are short lived and sensitive to minute changes in the environment 



