|Another of the physical characteristics used to identify wetlands
is the presence of hydrophytic vegetation. The term hydrophyte comes from the
Greek words hydro, meaning water, and phyton, meaning plant. The term
hydrophyte includes all aquatic and wetland plants. However, the term is
generally used to refer to vascular aquatic and wetland plants. Though
hydrophytes represent only a small percentage of the total plant population,
there are far too many to list here.
Upland plants normally have adequate soil oxygen available to the roots for use in the metabolic processes that convert food into energy. When soil saturation or flooding make oxygen unavailable, the metabolic process either stops altogether or shifts to anaerobic glycolysis, an enzymatic process that does not require oxygen to convert food into energy. Anaerobic glycosis produces much less energy than normal metabolic processes and causes an accumulation of toxic end products. Using anaerobic glycosis, most plants can produce only enough food to survive for short periods of time. Hydrophyticplants thrive in wetland soils in spite of the limitation or absence of oxygen because they are able to make special physiological adaptations.
Hydrophytic plants vary in the number of adaptations they exhibit, but generally those that exhibit a greater number of adaptations also exhibit greater tolerance to saturated soil conditions. Relatively few tree species, such as cypress and water tupelo, are able to make enough of these adaptations to tolerate flooding for more than a few weeks during the growing season. However, there are a number of species that exhibit one or more of these adaptations and thus tolerate varying degrees
|of soils wetness. Some plants such as green ash form
hypertrophied lenticels, enlarged structures on the above ground portion of the
plant that permit the exchange of gasses with the atmosphere facilitating the
transfer of oxygen from the air to the plant tissue. Green ash and northern
white?cedar grow large diameter, succulent roots at least partially composed of
cells with air spaces between them, called aerenchyma, which facilitate
movement of oxygen throughout the root tissue. Water hickory, black spruce and
balsam fir develop fibrous, lateral root systems which tend to spread
horizontally above the wetter soil levels. Larch, water hickory and water
tupelo develop adventitious roots, extra roots on the tree stem, again, above
the level of the wetter soil. Bald cypress and water tupelo develop a swelling
at the base of the tree which helps resist windthrow and may facilitate the
exchange of oxygen.
In some wetland adapted plants such as cordgrass, Spartina, the oxygen supply is large enough to cause oxygen to be diffused out through the roots oxygenating the rhizosphere, or outer surface of the root. Soil iron and manganese deposits in these areas are often oxydized by this method resulting in streaks of rust commonly seen in wetland soils.
Hydrophytic and other plants used to identify wetlands for regulatory purposes are listed in the National List of Plant Species that Occur in Wetlands, Biological Report 88(24), U.S. Department of the Interior, Fish and Wildlife Service. This publication lists five indicator categories for plants which can be found in wetlands: Obligate Wetland (OBL, > 99 percent occurrence), Facultative Wetland (FACW, 67?98 percent occurrence), Facultative (FAC, 37?67 percent occurrence), Facultative Upland (FACU, found in wetlands 1-33 percent of the time), and Obligate Upland (UPL, < 1 percent occurrence in wetlands in the area in question, but may be wetland plants in other regions). Abundant presence of species in the Obligate and Facultative Wetland indicator categories is a reliable indicator that a given tract of land is functionally a wetland. The absence of these species, however, is not a reliable indicator that an area is not a wetland, as these species may have been locally extirpated by severe disturbance or management.
The following is a list of some plants that commonly occur in wetlands in the Northeastern Area along with their indicator category for the northeastern region. This is not a comprehensive list, but merely a short list of readily identified plants the presence of which may indicate the need for further reconnaissance to determine if wetlands are present in the area. To be effective, a short list would have to be developed for a specific locale.
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