Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fr oblong to orbicular, laterally flattened, constricted at the commissure, the ribs filiform; oil-tubes in our sp. 3 in the intervals, 4 on the commissure; carpophore bifid to the base; umbels commonly 2 or 3 terminating the stem, with one or more lateral umbels below; bracts none or few and narrow; umbellets few-fld; bractlets few and narrow; sep triangular; pet white or pink; stylopodium ± conic; branching, glabrous perennials from fusiform or tuberously thickened roots; lvs pinnately decompound, or the uppermost once compound to simple. 15, mainly w. U.S., also one in e. Asia.