August, 1955 
(i.e., of much lower presence in other 
prairie types in Illinois) were Bouteloua 
curtipendula, Psoralea tenuiflora, Petalo- 
stemum candidum, Linum sulcatum, and 
Lithospermum incisum. 
14. Prairie stands possibly existed on the 
bluffs that now support prairie from Wis- 
consin or pre-Wisconsin time to the pres- 
ent. This vegetation will presumably con- 
tinue to grow on these sites until a change 
in climate occurs which will provide more 
mesic conditions, or until advanced erosion 
of the bluffs forms a continuously gentle 
slope, or until high cliffs are reduced. 
15. The observed flora of Illinois hill 
prairie was 394 species and varieties. Of 
these, 390 were vascular plants distributed 
in 209 genera and 70 families. The larg- 
est family was Compositae, with 26 gen- 
Evers: Hitt Prairies oF ILLINOIS 
443 
era and 71 species and varieties. Aster was 
the largest genus, with 12 species. Thirty 
species were of foreign origin. 
16. Although most species of Illinois 
hill prairie plants are of southeastern ori- 
gin, nine species are distinctly western or 
southwestern, and three are from the 
Ozark plateau. Of these 12 species, Ment- 
zelia oligosperma, Asclepias stenophylla, 
and Rudbeckia missouriensis are seemingly 
restricted to hill prairie and adjacent rock 
ledges. 
17. Some prairie slopes are grazed, and 
some are annually or less frequently 
burned, yet the prairie persists. As these 
steep slopes have never been plowed, they 
represent one of the least disturbed types 
of prairie in Illinois, and some of them 
should be preserved. 
