This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Amaranthus spinosus L. Sp. Pl. 991. 1753.
Rather dark green, glabrous or somewhat pubescent above, stem stout, erect or ascending, ridged, usually much branched, sometimes red, 1°-4° high. Leaves ovate, rhombic-ovate or the upper lanceolate, slender-petioled, acute at both ends, 1'-3' long, with a pair of rigid stipular spines 1/4'-1' long at each node, the midvein excurrent; flowers monoecious, the pistillate in numerous capitate axillary clusters, mostly shorter than the petioles, the staminate in dense terminal linear-cylindric spreading or drooping spikes 1'-6' long; bracts lanceolate-subulate about as long as the 5 scarious oblong mucronate-tipped 1-nerved sepals, and the thin imperfectly cir-cumscissile utricle; stamens 5.
Nearly or quite glabrous, rather pale green, stem diffusely branched, prostrate and spreading on the gorund, ridged, 6'-2° long, often forming mats. Leaves obovate or spatulate, 1/4'-1' long, obtuse or acute at the apex, narrowed into slender petioles, sometimes longer than the blades; flowers polygamous, in small axillary clusters mostly shorter than the petioles; bracts oblong to lanceolate-subulate, little longer than the 3 to 5 oblong-lanceolate acute or cuspidate sepals; stamens 3; utricle nearly smooth, circumscissile, equalling or slightly longer than the sepals.
In waste places, especially along the principal routes of travel, Maine to southern Ontario and North Dakota, south to New Jersey, Missouri and Kansas. Naturalized from west of the Rocky Mountains, where it appears to be indigenous from Washington to Utah, Colorado and Mexico. June-Oct.
Amaranthus graecizans L. Sp. Pl. 990. 1753. Amaranthus albus L. Sp. Pl. Ed. 2, 1404. 1763.
Glabrous, pale green, stem erect, bushy-branched, whitish, 6'-2° tall, the branches slender, ascending. Leaves oblong, spatulate or obovate, 1/2' - 1 1/2' long, slender-petioled, papillose, the midvein excurrent; flowers polygamous, several together in small axillary clusters shorter than the leaves, commonly not longer than the petioles; bracts subulate, pungent-pointed, spreading, much longer than the 3 membranous sepals; stamens 3; utricle wrinkled, circumscissile, longer than the sepals.
In waste and cultivated soil, throughout North America, except the extreme north. The leaves fall away in autumn, and on the western plains the plant, thus denuded, is freely uprooted and blown before the wind, whence the popular name. June-Sept.