53. ROSACEAE 123 



9. Lower surface of mature leaves sparsely pubescent along 

 the sides of the \eins with short, somewhat stifl' hairs; 

 corymbs sparingly pubescent; stamens 10 or 20, the fila- 

 ments short; thorns usually numerous, stout, 5-9 cm 

 long; fruit subglobose, nodding; banks of streams; 

 chiefly in the northern half of 111. May. [C. macra- 

 cantha Lodd.; C illinoiensis Ashe; C. corporea, divida, 

 gaultii, gemrnosa, laxiflora, longispina, rutila, vegeta 

 Sarg.] C. succulenta Schrad. 



9. Lower surface of leaves softly pubescent, especially on the 



veins; petioles wing-margined; corymbs tomentose; sta- 

 mens mostly 20, the filaments slender; thorns few, slender, 

 or none; fruit ellipsoid, erect; thickets and open woods, 

 generally distributed in 111., flowering in the latter part 

 of May and early part of June. [C. tomentosa sensu 

 auth., non L.; C. chapmani (Beadle) Ashe; C. structilis 



Ashe; C. hispidula, mollicula, whittakeri Sarg.] 



C. calpodendron (Ehrh.) Medic. 



8. Blades glabrous or essentially so; calyx-lobes entire. 



10. Leaves oval or rhombic, acute or acutish, the base cuneate; 



lower surface with tufts of tomentum in the axils of the 

 veins; styles and nutlets usually 5; alluvial soil; w. and 

 s. 111. [C arborescens Ell. ; C. atrorubens, durifolia, 

 schneckii Ashe; C. acutifolia, dawsoniana, erecta, in- 

 signis, larga, mitis, ovata, pechiana Sarg.; C. nitida 



(Engelm.) Sarg.] C. viridis L. 



10. Leaves short-obovate to suborbicular, usually incised with 

 shallow lobes, glabrous at maturity; styles and nutlets 

 2 or 3 ; thickets and open woods, not uncommon, from 

 Jersey, Macoupin, and Shelby counties northward. May- 

 June C. margarctta Ashe 



Leaves prevailingly widest below the middle or toward the sub- 

 cordate, truncate, rounded, or broadly cuneate base. 

 1 1 . Leaves glabrous or nearly so at maturity, or only slightly pubes- 

 cent beneath. 

 12. Leaves deltoid-cordate (often conspicuously 3- to 5-lobed) ; 

 calyx-lobes deltoid, entire; fruit 5-7 mm in diameter, 

 the calyx deciduous; chiefly s. 111., but extending north- 

 ward to Fayette Co. [C. cordata Ait.] 



C. phaenopyrum (L.f.) Medic. 



12. Leaves otherwise; calyx-lobes lanceolate; fruiting calyx 



usually persistent. 



13. Calyx-lobes entire or nearly so; inflorescence glabrous. 



14. Leaves thin, scabrellous on the upper surface when 



young, soon glabrous; stamens 10 or fewer; fiuit- 



ing calyx sessile; thickets, pastures, or open woods, 



usually near streams, n.e. 111. May. [C. coani, fer- 



rissii Ashe; C. apiomorpha, cyanophylla, dernissa, 



