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 elliptic, somewhat flattened laterally to subterete, the ribs narrowly winged; oil-tubes in our spp. 2–4 in the intervals, 6 on the commissure; carpophore bifid to the base, its halves sometimes ± adnate to the commissural face of the mericarps; umbels compound, mostly terminal, sometimes also lateral; bracts narrow and deciduous, or none; rays few to many, ascending; umbellets small, few-fld; bractlets few–several, linear; sep triangular; pet white; stylopodium low-conic; perennials from a taproot and/or branching caudex, with ternately or pinnately compound lvs. 20, mostly N. Temp.