for salt, indicating freshwater. This can be a valuable guide to the location of drinking and agricultural water in arid and semiarid areas. Examples of phreatophytes include Welwitschia and mesquite: Prosopis glandulosa. The alfalfa, or Medicago sativa, is a widespread phreatophyte plant of great economic value. Trees like the ash, the alder, the willow and the poplar are also useful in this regard. These trees generally grow in freshwater aquifers where the water table depth is not more than ten meters. These species are found in riparian ecosystems and areas characterized by shallow groundwater, such as bottomlands. They are also present in water limited environments; for example, oaks in the Mediterranean climate regions. See also Xerophyte Aquatic plant References Plant morphology Riparian zone Mediterranean forests, woodlands, and scrub