mesophytism. Since all vascular plants depend more or less upon water for their 

 very existence, and are thus biologically "aquatic" to a greater or lesser degree, 

 a premise to determine just how much effect a particular species has upon the 

 water resources of a given area could be carried to a ridiculous extreme. 



In the Introduction to his "A Flora of the Marshes of California," Mason has 

 expressed in unequivocable terms the way we feel about the limitation or lack of 

 limitation that should be placed upon plant species to be included in a work such 

 as this. We agree with him entirely when he says that the circumscription of the 

 field of research in this type of problem is not clear cut and that its boundaries 

 are usually highly artificial. We not only include the wholly aquatic species but 

 also the important and frequently critical amphibious species. But, as Mason 

 succinctly states, when we include ". . . . the amphibious species, we are drawn 

 immediately up on the shore, where the naturalness of the communities and the 

 overlapping of their species lead us farther and farther away from water." 



For convenience and simplicity, the term "vascular hydrophytes" has frequently 

 been used here to include both aquatic and wetland plants. 



I. Habitats of Aquatic and Wetland Vascular Plants 



Several outlines have been proposed to cover the various habitats in which 

 aquatic and wetland plants are to be found. For our purpose, and because it is 

 more far-reaching than most others, the one proposed by Mason, in 1957, is the 

 best yet devised. With some reorganization and the addition of several habitats 

 peculiar to our region, Mason's outline is as follows: 



I. Water standing or essentially so. 



A. Presence of water permanent and level fairly persistent. 



1. Open water surface the most conspicuous feature. 



a. Fresh water: lakes, ponds, reservoirs. 



b. Salt water: salt lakes, bays and oceans, estuaries, lagoons. 



2. Vegetation more conspicuous than water surface. 



a. Vegetation dominantly herbaceous. 



aa. Marshes: alkaline marshes, salt marshes, brackish marshes, fresh- 

 water marshes, 

 bb. Bogs: quaking bogs, floating bogs, evergreen shrub bogs. 



b. Vegetation dominated by trees and/or shrubs, 

 aa. Swamps, bay-galls. 



B. Presence of water intermittent or at least the level widely fluctuating. 



1. Intermittence seasonal: vernal pools, playa lakes, vernal marshes, 

 savannahs. 



2. Intermittence tidal: Salt-water marshes, seasonally salt and fresh-water 

 marshes, fresh-water marshes subject to tidal influence. 



II. Water flowing: live streams, intermittent streams, irrigation ditches, drain- 

 age canals, hillside bogs, streamside marshes. 



III. Wet soil adjacent to habitats with standing or flowing water: strand areas, 

 riparian lands, lacustrine lands, wet meadows, seasonally wet floodlands. 



There are very few natural lakes in southwestern United States, and these 

 are to be found mostly at high elevations in the mountains. Their creation is 

 solely the result of local conditions. The great ice sheets that formed lakes such 

 as those found in Wisconsin never reached this region. There are, however, 

 innumerable man-made lakes, reservoirs, ponds and stock tanks to be found in 

 southwestern United States, and many great and small rivers with numerous tribu- 



