Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Monoecious or dioecious; fls in cylindric catkins, the staminate longer and more loosely flowered than the pistillate; cal deeply 4-parted; stamens 4; style deeply 2-parted; fr a short-cylindric, edible syncarp resembling a blackberry, composed of juicy, accrescent but scarcely coherent calyces, each enclosing a small, seed-like achene, with the remains of the style protruding; trees with alternate, serrate or lobed (often mitten-shaped), palmately veined lvs. 10, widespread.