plants and tree seedlings in positions immediately above the 

 soil surface (e.g. Luduigia spp.) occur in response to inunda- 

 tion or soil saturation (Figure C3) . These usually develop 

 during periods of sufficiently prolonged soil saturation to 

 destroy most of the root system. CAUTION: Not all adventitious 

 roots develop as a result of inundation or soil saturation. For 

 example, aerial roots on woody vines are not normally produced 

 as a response to inundation or soil saturation. 



d. Shallow root systems. When soils are inundated or saturated for 

 long periods during the growing season, anaerobic conditions 

 develop in the zone of root growth. Most species with deep root 

 systems cannot survive in such conditions. Most species capable 

 of growth during periods when soils are oxygenated only near the 

 surface have shallow root systems. In forested wetlands, wind- 

 thrown trees (Figure C4) are often indicative of shallow root 

 systems . 



£. Inflated leaves, stems, or roots. Many hydrophytic species, 



particularly herbs (e.g. Lirrmobium spongia, Ludwigia spp.), have 

 or develop spongy (aerenchymous) tissues in leaves, stems, 

 and/or roots that provide buoyancy or support and serve as a 

 reservoir or passageway for oxygen needed for metabolic pro- 

 cesses. An example of inflated leaves is shown in Figure C5. 



f^. Polymorphic leaves. Some herbaceous species produce different 

 types of leaves, depending on the water level at the time of 

 leaf formation. For example, Alisma spp. produce strap-shaped 

 leaves when totally submerged, but produce broader, floating 

 leaves when plants are emergent. CAUTION: Many upland species 

 also produce polymorphic leaves. 



g. Floating leaves. Some species (e.g. Nymphaea spp.) produce 



leaves that are uniquely adapted for floating on a water surface 

 (Figure C6) . These leaves have stomata primarily on the upper 

 surface and a thick waxy cuticle that restricts water penetra- 

 tion. The presence of species with floating leaves is strongly 

 indicative of hydrophytic vegetation. 



h. Floating stems. A number of species (e.g., Altemanthera 



philoxeroides) produce matted stems that have large internal air 

 spaces when occurring in inundated areas. Such species root in 

 shallow water and grow across the water surface into deeper 

 areas. Species with floating stems often produce adventitious 

 roots at leaf nodes. 



i^. Hypertrophied lenticels. Some plant species (e.g. Gleditsia 



aquatvca) produce enlarged lenticels on the stem in response to 

 prolonged inundation or soil saturation. These are thought to 

 increase oxygen uptake through the stem during such periods. 



2_. Multitrunks or stooling. Some woody hydrophytes characteris- 

 tically produce several trunks of different ages (Figure CI) or 

 produce new stems arising from the base of a senescing indivi- 

 dual (e.g. Forestiera acuminata, Nyssa ogechee) in response to 

 inundation. 



C3 



