278 THE NORTH AMERICAN GRASSLAND 



ing these in the form of grassy openings. Owing to the large number 

 of common dominants and particularly subdominants, it forms a broad 

 ecotone with the true prairie to the north, with the general boundary 

 rather southward of the Texas line. In the direction of the Panhandle, 

 it passes gradually into the mixed prairie, and along the extended 

 western line it comes in touch with the desert plains grassland of 

 western Texas and adjacent Mexico. Along the shores of the Gulf it 

 is bordered by a narrow band of subclimax coastal marsh, more or 

 less interrupted or paralleled by coastal dunes (Tharp, 1926). 



Climate. By reason of its proximity to the Gulf, the coastal 

 prairie is signalized by higher rainfall than any other association of 

 the grassland; it is also warmer than any except the desert plains, and 

 evaporation bears a corresponding relation. Perhaps the most sig- 

 nificant feature is the relatively warm winter over much of the area, 

 which favors the presence of subtropical dominants. Toward the 

 northwest, however, the climate rapidly becomes continental in type, 

 with an extreme range from zero to 110° F., and with a striking change 

 in faciation as a consequence. 



Dominants. The dominants of this prairie are the following: 



Stipa Icucotricha Bouteloun curtipendula 



Andropogon saccharoides Sporobolus asper 



sc.oparius berteroanus 



furcatus Agropymm smithi 



contortus Koeleria cristata 



ternarius Aristida purpurea 



nutans Buchloe dactyloides 



Trachypogon montufari Hilaria ccnchroides 



Elyotnirus iripsacoides Bouteloun texaria 

 Manisuris cylindrica trifida 



Paspalum plicatulum hirsuta 



Panicum virgatum Triodia pilosa 



The generally subtropical nature of this association is shown by the 

 presence of 9 species of Andropogoneae, while other southern deriva- 

 tives number as many as 6, such as Stipa leucotricha, Sporobolus ber- 

 teroanus, Hilaria cenchroides, and Bouteloua texana. Five dominants 

 are possessed in common with the true prairie, 6 with the mixed 

 prairie, and 7 with the desert plains. The eudominants are Stipa 

 leucotricha, Andropogon saccharoides, Trachypogon, Elyonurus, Mani- 

 suris, and Bouteloua texana. 



Owing to the long growing season and favorable rainfall, the dis- 

 tinction between tall and mid grasses is somewhat less clear than 

 further north, but in general the three groups of the list represent 

 tall, mid, and short grasses. By far the larger number belong to the 



