A vast ecosystem of wetlands and lakes once covered the Mesopotamian Plain of southern Iraq. Widespread drainage in the 1990s nearly obliterated both components of the landscape. This paper reports the results of a study undertaken in 1972-1975 on the vegetation of the wetlands prior to drainage and provides a unique baseline for gauging future restoration of the wetland ecosystems in Mesopotamia. Five representative study sites were used to assess the flora, three of which were wetlands. A total of 371 plant species were recorded in the five sites, of which approximately 40% represent obligate or facultative wetland species. The wetland vegetation was classified into five major physiognomic forms (submerged, floating, herbaceous tall emergent, herbaceous low emergent and woody low emergent), which was further subdivided into 24 fresh and halophytic communities. Water levels greatly fluctuated across the different types of wetlands, and mean surface water depth ranged from below to greater than 2 m above the sediment surface, reflecting permanently, seasonally or intermittently wet habitats. Aboveground biomass was also highly variable among the communities. The Phragmites australis community, which was the most extensive community type, had the greatest biomass with an average value of approximately 5,000 g m-2 in summer. Distribution and community composition were largely controlled by water levels and saline-freshwater gradients. Canonical correspondence analysis showed that salinity and water depth were the most important factors to explain species distribution. Environmental variables related to soil salinity separated halophytic species in woody low emergent and herbaceous low emergent forms (Tamarix galica, Cressa cretica, Alhagi mannifera, Aeluropus lagopoides, Juncus rigida, and Suaeda vermiculata) from other species. Their habitats were also the driest, and soil organic matter content was lower than those of other species. Habitats with deepest water were dominated by submerged aquatic and floating leaved species such as Nymphoides peltata, Ceratophyllum demersum, and Najas armata. Such diverse environmental conditions in the Mesopotamian wetland would be greatly affected by evapotranspiration, river water inputs from north, ground water inputs, local soil conditions, and a tide or seiche-controlled northward transgression of water from the Gulf. These environmental conditions should be considered in restoration plans if plant communities existed in the mid-1970s are to be part of the desired restoration goals.