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Hydrophytic vegetation is the final parameter of the wetland definition. In general terms, hydrophytic vegetation is plant-life that thrives in wet conditions. More technically put, the term hydrophytic vegetation, as it relates to wetland identification, is defined as, "the sum total of macrophytic plant life that occurs in areas where the frequency and duration of inundation or soil saturation produce permanently or periodically saturated soils of sufficient duration to exert a controlling influence on the plant species present" (U.S. Army Corps of Engineers 1987).

In conjunction with the National Wetlands Inventory (NWI), a nationwide effort to map all of the wetlands in the United States, the U.S. Fish and Wildlife Service (USF&WS) has developed a National List of Plant Species that Occur in Wetlands. According to this list, there are five categories in which plant species that appear in wetlands may be placed. These categories are as follows:

  • Obligate (OBL)-Occur almost always (estimated probability >99 percent) under natural conditions in wetlands.
  • Facultative Wetland (FACW)-Usually occur in wetlands (estimated probability 67-99 percent), but occasionally found in non-wetlands (estimated probability 1-33 percent).
  • Facultative (FAC)*-Equally likely to occur in wetlands or non-wetlands (estimated probability 34-66 percent).
  • Facultative Upland (FACU)-Usually occur in non-wetlands (estimated probability 67-99 percent), but occasionally found in wetlands (estimated probability 1-33 percent).
  • Upland (UPL)-Occur almost always (estimated probability >99 percent under natural conditions in non-wetlands

* Those plant species classified as Facultative can further be classified as FAC+ or FAC-. This designation reflects the regional frequency of occurrence of that species in wetlands. A FAC+ species is one that is more frequently found in wetlands in a specific region, whereas a FAC- is found in wetlands less frequently (Reed 1988).

When making a wetland determination and/or delineation, emphasis is placed on the total assemblage of dominant macrophytic plant species rather than on the presence of a particular indicator species. Thus, "the presence of scattered individuals of an upland plant species in a community dominated by hydrophytic species is not a sufficient basis for concluding that the area is an upland community. Likewise, the presence of a few individuals of a hydrophytic species in a community dominated by upland species is not a sufficient basis for concluding that the area is a wetland community" (U.S. Army Corps of Engineers 1987).

Without a background in botany, it may be difficult for an individual to discern if the plant communities present are indicative of a wetland or upland landscape. Even if an individual can not taxonomically name the plant species in a particular area, there are some clues one can look for which will help identify many plant species as hydrophytic. To survive in anaerobic, hydrologic conditions, many plants have developed some obvious physical adaptations to facilitate the capturing and transporting of oxygen. Some of these adaptations include:

Most people associate plant species such as cattails, waterlilies, and duckweed with wetland areas, but require additional information to identify other obligate wetland species such as buttonbush, bulrush, and arrowhead. IDNR has in the past published a Field Guide to the Wetlands of Illinois (now out of print) which has full color photographs, classifications, and detailed descriptions of 100 of the most common wetland plants in Illinois. This paperback book is an excellent resource for individuals interested in learning how to identify wetland vegetation. It also contains color photographs, classifications, and detailed descriptions of 13 different "typical" Illinois wetland types (Illinois Department of Natural Resources 1988). Contact your local library to see if it has a copy.


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