54 American Midland Naturalist Monograph No. 7 



leaves lanceolate; plants perennial; swamps or 



ditches, local, chiefly in s. 111. June-Aug 



R. anibigens Wats. 



7. Basal leaves reniform or cordate, merely crenate (some 

 of the later ones often lobed or cleft) ; stem-leaves 

 cleft or lobed; achenes minutely beaked, in globose 

 heads. 



10. Petals much longer than the sepals. 



1 1 . Basal leaves oval or ovate, not cordate ; stamens in 

 3-5 series; sepals long-villous; prairies, n. 111.; 

 rare, Jo Daviess, McHenry, and Winnebago 

 counties. May. Prairie Buttercup [R. ovalis 

 Raf.] R. rhomboideus Goldie 



1 1 . Basal leaves reniform or orbicular, cordate ; 

 stamens in 1-2 series; sepals sparsely pilosulous; 

 sandstone ravines, rare, s. 111.; Jackson and 

 Randolph counties, R. H. Mohlcnbrock in 1954 



and 1957. April-May 



R. harveyi (A.Gray) Britt. 



10. Petals somewhat shorter than the sepals; flowers less 

 than 1 cm in diameter; plant glabrous or nearly so; 

 moist ground, very common. Apr. -May. Small- 

 flowered Buttercup R. abortivus L. 



6. Leaves all or nearly all lobed or divided. 



12. Achenes muriculate; flowers axillary; waste ground; 

 native of Eur.; Jackson Co., R. H. Mohlcnbrock 



2437 in 1954 R. parviflorus L. 



12. Achenes smooth (or sparsely tuberculate in R. sardous) ; 

 flowers mostly terminal. 

 13. Petals not longer than the sepals; flowers less than 

 1 cm in diameter. 



14. Stem glabrous or nearly so, hollow; achenes 

 merely apiculate, in ellipsoid heads; along 

 ditches, locally nearly throughout 111. May- 

 July R. sceleratus L. 



14. Stem usually pubescent. 



15. Basal leaves usually 3-lobed; woods, not com- 

 mon; chiefly s. 111., n. to Shelby and 



Cumberland counties. Apr.-May 



R. lyiicranthus Nutt. 



15. Basal leaves deeply parted or divided. 



16. Leaf-divisions merely serrate; heads of 

 achenes globose, the achenes with 

 slender, hooked beaks; woods. Apr.- 

 June R- recurvatus Poir. 



