Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fr oval, oblong, elliptic, or orbicular, usually flattened dorsally, the lateral and often also the dorsal ribs evidently winged, or the ribs sometimes all merely elevated and corky-thickened; carpophore bifid to the base; umbels very large, compound; bracts none or few and linear; rays many; umbellets densely many-fld; bractlets linear or filiform; sep minute or none; stylopodium broadly conic; pet in ours white or greenish-white; stout, taprooted, usually single- stemmed perennials with long-petioled, pinnately decompound basal lvs and progressively reduced upper lvs, the uppermost often bladeless, the lfls otherwise broad and toothed or cleft. 50, circumboreal.