4 American Midland Naturalist Monograph No. 2 



disappeared. However, the original prairie has all but vanished from the Illinois 

 landscape, and no typical area of upland prairie remains for botanical study. 

 Extensive tracts of these upland prairies were swampy, but almost all have 

 been drained and their natural vegetation has since disappeared except from 

 roadsides and along the railroads. Other areas are covered chiefly with sand 

 or sandy loam, and support a flora of psammophilous species, including Lepto- 

 loma cognatum, Tephrosia virginiana, Helianthemum canadense, Oenothera 

 rhombipetdla. Phlox bifida, Lithospermiim croceiim, and Chrysopsis rillosa. 

 The principal sand-areas are in the northern half of the state. 



Statistical summary. — The total known number of native and naturalized 

 species of vascular plants growing spontaneously in Illinois is 2124. Of this 

 number, 1786 are indigenous, and 338 have been either adventive or intro- 

 duced, and are now more or less established. Trees and shrubs belong to 49 

 families, 111 genera, and 302 species. Salix has 17 species and Quercus 19. 

 In the genus Crataegus, 14 species are recognized as occurring within the boun- 

 daries of the state. Herbaceous plants belong to 113 families, 713 genera, and 

 1822 species. Carex is the largest genus with 114 species. There are 70 genera 

 and 215 species of grasses, of which 166 species are native. Panicum is the 

 largest genus of grasses with 36 species. Twelve genera and 26 species of 

 orchids are recorded for Illinois. Compositae is the largest family, with 63 

 genera and 243 species. Aster is the largest genus in this family with 34 

 species; Solidago comes next with 22 species. For a "prairie state" there is a 

 surprisingly large number of ferns and fern-allies, and the number of species of 

 ligneous plants is remarkably high. 



Families Genera Species 



Ferns and fern-allies 10 29 63 



Gymnosperms 4 7 11 



Monocotyledons 22 154 575 



Dicotyledons 116 526 1475 



Total 152 716 2124 



Vegetational Divisions 



The spontaneous flora of Illinois comprises a vegetation thit is rather 

 sharply differentiated into prairie and forest. Each of these two types of 

 vegetation includes a number of communities or associations, reflecting the 

 transitions in tcmp'erature and minfall, ns well as the topographic and ednphic 

 conditions. On the accompanying map the eco'o:;ical divisions are based prin- 

 cipally upon the broader topographical features, including the effects of glacial 

 geology. The area affected by the recent (Wisconsin) glaciation is mostly 

 treeless, and extensive areas of upland prairie formerly occurred in the 

 western division. It will be noted that the botanical areas are correlated with 

 the various agricultural districts, and are thus intimately conn'ected with vari- 

 ous phases of human geography. Moreover, it is obvious that faunal areas 

 parallel the natural botanical divisions, and thus these divisions are useful to 

 zoologists, as well as to students of the applied branches of biology, including 



