August. 1955 



EvERS: Hii.i. Prairies of Illinois 



393 



lata, and Sorghastntni nutans. Thus, in 

 50 per cent or more of the hill prairies, 

 there were 25 species present. All are na- 

 tives of North America except one, possi- 

 bly r\vo. .Melilotus alba is Eurasian. Poa 

 pratensis is generally considered European 

 by many authorities, but Gleason (1952) 

 states, "In most of our range introduced 

 from Europe: along our n. boundari,' and 

 in Canada it may be nati\e." It might 

 prove difficult to determine whether Illi- 

 nois plants of this species had their origin 

 in Europe or Canada. 



Species most characteristic of the hill 

 prairie type are Bouteloua curtipendula, 

 Psoralea lenuiftora, Petalostemum can- 

 diduni, Liniirn suhatuin, and Lithospei-- 

 mttm incisuiii. The presence of these spe- 

 cies in other prairie types in Illinois is 

 much lower than in hill prairie. 



Seasonal Aspect. — The Illinois hill 

 prairies studied in the years covered by 

 this report showed certain seasonal as- 

 pects. 



In winter, the brownish color of the 

 grass cover predominated. On some un- 

 grazed hill prairies, tall grass stems of 

 the previous growing season bent over and 

 trended downslope to form a fairly com- 

 plete cover over the soil. Small purplish 

 rosettes of S'tlidago nanoralis and green 

 rosettes of Senecio plattensis were evident 

 between the grass clumps in some of the 

 prairies. 



The prevernal aspect was mostly 

 brown. In early April in some prairies, 

 the small white flowers of Draba reptans 

 were seen. By late April, the violet flow- 

 ers of Oxalis vio'acea, the yellow-orange 

 blos-oms of Lithosperniiim canescens, and 

 the yellowish flowers of Salix hinnilus and 

 Rhus aroniatica were evident among the 

 grass bunches. 



In the vernal phase, the dominant color 

 changed from brown, through brownish- 

 green, to green as the grasses began their 

 growth. Hedeonia hispida. with very 

 small bluish blossoms, was common in the 

 interspaces in many prairies. Erigeron 

 strigosus, taller than the grasses during 

 the vernal phase, was very conspicuous 

 with its -white flowers, as was also Pen- 

 stemon pallidus. Tradescan/ia, with pur- 

 ple blooms raised abo\e the level of the 

 grasses, was scattered in man\ prairies. 



The yellow rays of Senecio plattensis and 

 Coreopsis layceolata were conspicuous in 

 some. Several grasses, Panicurn scrib 

 nerianum, Poa pratensis, Festuca octo- 

 flora, and Koeleria cristata, flowered at 

 this time. 



In the aestival stage, the predominating 

 color was green or purplish-green. Echi- 

 nacea pallida, with purplish rays, was in 

 bloom, and Linum sulcatum, with small 

 yellow petals, began its flowering. In 

 some prairies the small whitish flowers of 

 Houstoiiia nigricans were frequent. The 

 inflorescences and foliage of Psoralea 

 tenuiftora gave some prairies a purplish- 

 green hue, especially in early July. The 

 purple-flowered Buchnera americana and 

 Petalostemum purpureum and the white- 

 flowered prairie-clover, P. candidum. were 

 scattered in some prairies. In late June 

 and early July, the green or purplish- 

 green inflorescences of Bouteloua curti- 

 pendula appeared. In the latter part of 

 July and early August, the bronze, green, 

 or purplish-green inflorescences of An- 

 dropogon scoparius and A. gerardi were 

 conspicuous. B\ late August, the yellow 

 of Solidago nemora'is and the purple of 

 Liatris asp era were evident. 



In the autumnal phase, beginning in 

 September, the dominant color changed 

 from green to brownish hues. The yel- 

 low rays of Solidago nemoralis and the 

 white or purple rays of several species of 

 Aster were common. By October, very 

 few plants, an occasional Solidago or a 

 Houstonia, or, less often, a Spiranthes, 

 were still in flower. By November the 

 prairie was again dormant ; the dominant 

 grass cover was brown. 



\ EGETATIONAL HISTORY 

 AND SUCCESSION 



The vegetational history of Illinois, a 

 state that is within the area of overlap 

 of eastern prairie and forest, is deduced 

 mainly from circumstantial e\ idence. The 

 evidence is derived from the present flora 

 and vegetation, especially from apparent 

 relict colonies, from fossils in the loess, 

 and from analyses of pollens and fossils in 

 peat and lacustrine deposits. Deductions 

 must conform not onl) to the facts of bot- 

 an\ but also to the facts of meteorology' 



