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..
Stems globose, leafless, tubercled, the tubercles arranged in spiral rows bearing clusters of spines arising from areolae. Flowers borne on the tubercles, at or near areolae from which spines are developed. Calyx-tube prolonged beyond the ovary, its tube funnelform, bearing a few scales. Petals numerous, similar to the inner sepals, but larger, pinkish. Stamens numerous, borne on the tube of the calyx. Ovary green, globose; style columnar. Berry irregularly bursting, with a terminal scar, nearly or quite scaleless. Seeds tubercled, with a large sub-basal hilum. [Greek, Plains-cactus.]
Three species, natives of central and western North America, the following typical.
Stems single, globose or with a narrowed base, 3'-6' high, 3-4' in diameter. Tubercles ovoid, somewhat 4-sided at base, 6"-8" long, arranged in spirals; central spines yellowish below, nearly black above, 5"-7" long, the exterior ones slightly shorter, whitish; flowers greenish pink, 8"-10" long and about as broad, borne to one side at the ends of the tubercles; petals oblong, crenulate and cuspidate at the apex; berry dry, 3"-3" in diameter, bearing near its summit 2-3 scales which sometimes have short spines in their axils.
Kansas (according to B. B. Smyth); Colorado to Wyoming, Utah, New Mexico and Nevada. April-May.