The descriptions of families and genera, while they definitely include the plants 

 in our area, have, in many instances, been written so as to include plants that 

 might eventually be found in southwestern United States. 



In giving habitat data for the species, in most cases only habitats that fall within 

 the province of our interest are given. In other words, in the case of those species 

 that are tolerant to a wide range of habitats only the aquatic or wetland habitats 

 are usually cited. 



We early realized that the scope of our work could become prodigious, especially 

 when we discovered that similarly appearing habitats in proximity more frequently 

 than not had a dissimilar floral composition. This meant that if we expected to 

 obtain a complete knowledge of the occurrence and distribution of species within 

 our region it would be necessary for us to investigate as many localities as possible 

 in a given area rather than to depend solely upon random sampling in few specific 

 localities. 



We also realize that there are distinct possibilities that some researchers or 

 otherwise interested individuals may find species that they consider should have 

 been included in this work. These omissions could be due to a number of reasons, 

 foremost of which would be a lack of information or a difference in interpretation 

 as to what should or should not be included, or to an oversight on our part. If 

 such an omitted species is found we recommend that its identity be sought in some 

 one of the standard Floras that covers the particular region in which the plant 

 is found. These Floras are cited in the Bibliography. 



It is also possible that some of our colleagues may question our inclusion of 

 certain species, especially the woody ones. Among these might be Cephalanthus 

 occidentalis, Gleditsia aquatica, Nyssa aquatica, Salix spp., Quercus spp., Platanus 

 spp. and Tamarix spp. Since this treatise is not solely a biologic one but is also 

 concerned with the economics of water and its utilization by plants, species such 

 as the above have been included. Also, since they grow either directly in water, in 

 saturated soils or along water courses they must be considered to be heavy users 

 of water. The same principle is applied for the inclusion of plants that grow in 

 such places as alpine and subalpine wet meadows, on seepage slopes below snow- 

 fields, and in seepage along streams and about springs. These plants draw heavily 

 upon the very source of water that ultimately makes up the streams and rivers at 

 lower elevations. They also form turf that aids in the control of water flow from 

 such places. 



When originally proposed, this project was intended to be concerned with 

 aquatic and wetland plants in every type of habitat that fitted into these categories. 

 However, when support was first obtained from the National Institutes of Health, 

 officials of that agency suggested an administrative change for the title so as to 

 be more in line with the work and purpose of their organization. The title change 

 was to be "Aquatic and marsh plants of polluted waters in southwestern United 

 States." With this new title, we considered having the subtitle read "Paludal 

 Plants of Polluted Places." 



So as to live up to the administrative title as much as possible we have paid 

 particular attention to the sewage effluents from small and large cities, essentially 

 open cesspools of villages and small towns and even the seepage from large septic 

 tanks of motels, homesite developments and other such places that often were 

 flowing into lakes within a few yards of beaches where children and their parents 

 were playing and swimming. We never felt delinquent when we worked along 

 rivers or streams, and in and about lakes and other impounded waters, because we 

 realized that we were still working within the administrative bounds of our 

 project. We considered unpolluted only those streams and water bodies from which 

 we could drink directly. Needless to say, we would have perished from thirst if we 



