197] FLORA OF COLUMBIA AND VICINITY 55 



b. Agrestes vemonioides. The ironweed association 

 of wild and half-wild fields consists of certain prairie plants 

 together with the usual pasture grasses and weeds. Such fields 

 are pseudo-prairies. The vegetation is much alike in all, con- 

 sisting of the fleabanes {Erigeron animus, E. ramosus, and E. 

 Canadensis) , Rudbeckia liirta, Teucrium Canadense, Verbena 

 stricta, Koellia Virginica, Eupatorium serotinum, Vernonia 

 Baldminii, V. maxima, V. interior, and the common pasture 

 weeds Cirsium lanceolatum, Verbascum Thapsus, Gnaphalium 

 obtusifolium, etc. Triodia cuprea and Eragrostis pectinacea are 

 characteristic grasses in autumn. 



III. XEBOPHYTES. 



The xerophytic vegetation of the region falls into two pri- 

 mary zones, the zone of cliflfs, and the zone of barrens. To 

 these is to be added a third zone, that of the cliff and bluflf 

 prairies. These zones are poorly differentiated, all three ming- 

 ling occasionally at the summits of cliffs. Much of the vegeta- 

 tion is mesophytic, but therein is comprised nearly all our gen- 

 uinely xerophytic species. On hills and knolls in woods and 

 thickets occur also a few xerophytic plants, and as we have seen, 

 the shore sands support a xerophytic growth. 



A. RuPESTRES. Plants of the cliff zone. 



The rupestrine flora gives to the region its stamp of in- 

 dividuality. Many of the plants are endemic to the limestone 

 cHffs of Missouri and the neighboring states. The flora has 

 not come from other regions, it has developed here, and no other 

 species successfully invades its peculiar habitat, if there be ex- 

 cepted a few weeds, such as the mullein {Verbascum Thapsus). 

 Because of its endemic character it is a vanishing flora. Many 



