130 American Midland Naturalist Monograph No. 2 



10. Stem glabrous or nearly so, hollow; acbencs merely apiculate, 

 in ellipsoid heads; along ditches, in the n. half of th? state. 

 May-July. Celery-leaved Buttercup R. sceleratus L. 



10. Stem pubescent. 



11. Basal leaves slightly lobed; achenes with a short, recurved 

 beak, in globose heads; woods, s. 111., not common. Apr.- 

 May R. micranthus Nutt. 



11. Basal leaves deeply parted or divided. 



12. Leaf-divisions merely serrate; heads of achenes globose, 

 the achenes with slender, hooked beaks; woods. Apr.- 

 June R. recurvatus Poir. 



12. Leaf-divisions cleft or incised; heads of achenes ellip- 

 soid, the achenes with short nearly straight beaks; wet 

 ground. July-Aug R. pennsyhanicus L. £. 



9. Petals longer than the sepals; flowers 1.5-2.5 cm. in diameter. 



13. Beak of the mature achene less than 1 mm. long, recurved. 

 14. Stem more or less cormose-thickened at base; leaves with 

 the terminal division stalked; sepals reflexed; fields and 

 roadsides, adv. from Europe. May-July. Bulbous Butter- 

 cup R. bulbosus L. 



14. Stem not swollen at base; leaves with all the divisions ses- 



sile; sepals spreading; roadsides and fields, adv. from 

 Europe. May-July. Tall Buttercup R. acris L. 



13. Beak of the mature achene 1 mm. or more in length. 



15. Petals broadly obovate; plants stoloniferous. 



16. Beak of the achene curved; mature achene 2-2.5 mm. 

 in diameter; roadsides and fields, comm.on; adv. from 



Europe. Apr.-June. Creeping Buttercup 



R. repens L. 



16. Beak nearly straight; mature achene 3-3.5 mm. in diam- 



eter; wet woods, common. Apr.-June. Marsh Butter- 

 cup R. septejitnonalis Poir. 



15. Petals oval or narrowly obovate; achenes 2-2.5 mm. in 

 diameter; plants not stoloniferous. 



17. Stem strigose; leaf -lobes narrow; root tuberous-thick- 



ened; woods and meadows. Apr.-May. Tufted Butter- 

 cup R. fascicularis Muhl. 



17. Stem villous; leaf-lobes oval to oblanceolate; roots not 

 thickened; woods or roadsides. Apr.-May. Bristly 

 Buttercup R. hispidus Michx. 



10. Thalictrum L. — Meadow-rue 



1. Leaflets glabrous on both surfaces. 



2. Leaflets thin, suborbicular in outline, obtusely 5-9-lobed; stem-leaves 



