Fish and Wildlife Service and developed in cooperation with a federal inter-agency review panel (Reed, 1988).
In some instances the specified regions contain all or part of different floristic provinces and the tension zones which occur between them.
Plant species are general indicators of various degrees of environmental factors; they are however not precise.
The presence of a plant species at a specific site depends on a variety of climatic, edaphic and biotic factors, and the effect of individual factors such as degree of substrate saturation and depth and duration of standing water is impossible to isolate.
The (+) sign indicates a frequency towards the wetter end of the category (more frequently found in wetlands) and the (−) sign indicates a frequency towards the drier end of the category (less frequently found in wetlands).