Frequent throughout the state in rich woods and infrequent in prairie habitats, preferring alluvial soil along streams and wooded slopes. This species is extremely variable in all of its parts and the form with narrow leaf-segments has been named. Plants that grow in rich soil in shady places usually have the leaf-segments large and ovate while plants that grow in poor soil and prairie habitats usually have the leaf-segments narrow. The nodes, peduncles, umbels, and furrows of the fruit are generally more or less pubescent with short, stout, colorless hairs (sometimes only granulose). The nodes are always pubescent and rarely can a plant be found that has the inflorescence nearly glabrous. Sometimes the pubescence is conspicuous in the inflorescence and on the veins of the lower surface of the leaflets. The flowers are sometimes cream-colored, and the fruit varies in size and pubescence. I am not able to correlate the pubescence with any other character and have concluded that we have a polymorphic species whose variations are due to soil and exposure.
Stem to 1 m, branched above, pubescent around the upper nodes with minute stiffish hairs; basal and principal cauline lvs twice pinnate or ternate- pinnate, the lfls ovate to lanceolate, serrate to incised; umbels commonly 3-6 cm wide, at anthesis scarcely surpassing the lvs, the 8-16 rays subequal; fls pale yellow or cream-color; bractlets linear, acute, 1-4 mm; fr glabrous, ellipsoid, 4-6 mm, the lateral and some of the dorsal and intermediate ribs broadly winged; 2n=22. Woods and prairies; N.Y. and Ont. to Minn., s. to Fla. and Okla. May, June.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.