Amaranthus spinosus L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Monoecious; stem erect, branched, to 1 m, bearing at most nodes a pair of divergent spines 5–10 mm; lvs lance-ovate to ovate, 3–6 cm, narrowed to an obtuse, mucronate tip, broadly cuneate to the long petiole; spikes numerous, 5–15 cm, 6–10 mm thick, the terminal often chiefly or wholly staminate, the basal part and the axillary clusters mostly pistillate; sep of the pistillate fls 5, oblong, 1–1.5 mm; fr 1.5–2 mm, indehiscent or bursting irregularly, the terminal part spongy and roughened; seed suborbicular, 0.7–1 mm; 2n=32, 34. A pantropical weed, probably originally from the New World, extending n. in our range to N.Y., Pa., Ind., and Mo., seldom farther n.