Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Staminate catkins slender, elongate, borne in peduncled groups of 3 at the summit of the previous year’s growth or at the base of that of the current year; "perianth" 2–3-lobed, closely subtended and usually surpassed by the bract; stamens 3–10, commonly 4; anthers pilose; pistillate fls solitary or in spikes of 2–10, terminating the branches, each closely subtended by a cup-shaped, 4-lobed, perianth-like involucre that ripens with the fr to form a husk; tepals obsolete, husk ± dehiscent into 4 valves, releasing the hard shelled nut; trees with hard, heavy wood, continuous pith, and odd-pinnate lvs, the 3 terminal lfls usually the largest; lfls with involute vernation. (Hicoria) 15, e. N. Amer. and e. Asia.