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 ovoid, cylindric or oval, ribbed, or tubercled, the ribs or rows of tubercles usually straight, mostly vertical; leaves none. Spine-bearing areolae on the ribs or tubercles. Flowers borne on the ribs or tubercles, at or near the areolae, close to fully developed clusters of spines. Calyx-tube with spine-bearing areolae, or scaly, prolonged beyond the ovary. Fruit spiny. [Greek, hedgehog-Cereus.]
About 65 species natives of America. Besides the following, some 30 others occur in the southwestern United States. Type species: Echinocereus viridiflorus Engelm.
Flowers greenish, about 1' broad; fruit s"-6" long.
Echinocereus viridiflorus Engelm. Wisliz. Tour North. Mex. 91. 1848.
Cereus viridiflorus Engelm. Mem. Am. Acad. (II.) 4: 50. 1849.
Stem subglobose to oval-cylindric, 1'-8' high, simple, or sparingly branched, 1'-2' in diameter. Ribs about 13; longer radial spines 12-18, with 2-6 setaceous upper ones, the lateral ones reddish brown, the others white or rarely purple; central spine stout, straight or curved, purple and white, or wanting; flowers about 1' broad, greenish brown without, yellowish green within; petals obtuse or acute; fruit ellipsoid, greenish, 5"-6" long; seeds tubercled.
South Dakota to Wyoming, Texas and New Mexico. Our figure is copied from plate 36, Cactaceae of the Mexican Boundary Survey, representing the Cereus viridiflorus tubulosus Coult. Contr. Nat. Herb. 3: 383. 1896.
Echinocereus caespitosus Engelm. Wisliz. Tour North. Mexico, no. 1848.
Stems ovoid-globose to ovoid-cylindric, usually tufted, sometimes as many as 12 together, sometimes single, 1'-6' high, 1'-4' in diameter; ribs 12 or 13; radial spines 20-30, pectinate, white, the lateral ones the longer, 2"-4" long; central spines wanting, or sometimes 1 or 2 short ones; flowers rose-purple, 2-3' broad, fruit ovoid, green, 9"-10" long; seeds tubercled, black, about i" long.
Western Kansas (according to B. B. Smyth); Texas and Mexico.