This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
Globose or depressed-globose, 10-16 in. diam.: ribs about 21, very acute and wavy (not tuberculately interrupted): radial spines 6-10, white and comparatively slender, or wanting; centrals red and very robust, angular-compressed, with long, sharp, horny tips, the upper 3 erect-spreading, 1-1 1/2 in. long, the lower 2 weaker and declined, the central one longer, more rigid and keeled, very broad (1/5-1/3 in ) and hooked downward: flowers purple, 1-1 1/2 in. long. Mex.
Ovate or at length subcylindric, becoming 4-10 in. high and 3-4 in. diam.: ribs 13-17, obtuse, tuberculately interrupted: radial spines 20 or more, compressed and white, the uppermost wanting, the 4 upper ones broader and longer (1-2 in.) and dusky-tipped, the laterals shorter (4/5-l in.), the lowest very short (1/2in.) and subsetaceous; central spines of several forms, the uppermost one (rarely a second similar but smaller one above or beside it) compressed-quadrangular, elongated (3-5 in.), white with dusky tip, curved upward, the other 5-10 teretish or subangled, bright purple-brown; upper ones long (2-4 in.) and mostly straight, the others gradually shortening (to about 1 in.) downward and sharply hooked: flowers red or yellow, 2-2% in. long and wide. Nev. and S. E. Calif.
aa. Spines not hooked (Nos. 11-48). b. Central spines none or indistinct.
Stout, globose and bright green: ribs 13-17, tuberculate, broadest toward the base, undulate; tubercles somewhat hexagonal, strongly dilated below: radial spines 9-12, the lower ones somewhat longer, very stout, spreading, yellowish translucent, reddish at base; central wanting: flowers varying from white to yellow and red. Paraguay.
Oblong-globose, becoming 1-2 ft. high and 1 ft. diam.: ribs 11-13, compressed and somewhat acute: spines 6, about equal, rigid, straight, divergent or erect, pale transparent yellow with a brownish base; very rarely a solitary central spine. Mex.
Depressed, from a large indurated naked napiform base, 2-4 in. across the top: ribs 10-15, acute from a broad base, more or less transversely interrupted and sinuous: spines 3, annulate, very stout and erect from deeply sunken areoles, reddish when young, becoming ashy gray; upper spine stoutest, erect and straight, or slightly curved upward, flattened and keeled, and occasionally twisted, l 1/2-2 1/4 in. long; the 2 laterals erect-divergent, straight or slightly curved, terete above and somewhat quadrangular below, 1-1 1/2 in. long; all from an abruptly enlarged base: flowers said to be small and white, with purplish median lines. Mex.
Depressed-globose: ribs very numerous, 90-120, compressed into thin plates which run vertically or are twisted in every direction: spines exceedingly variable, in some cases wanting entirely, in others 3 or 4, short, rigid, and translucent yellow; in others more numerous, larger, and often flattish; in still other cases very long and flat, interlacing all over the plant; no centrals: flowers white, with a broad purple stripe. Mex.
Globose: ribs about 11, broad, spotted all over with white dots: clusters of spines distant, usually seen only near the apex; spines 5-10, long and flexuous; centrals not distinct: flowers large, yellow. Mex.
Cylindrical, covered with ivory-white spines which are tipped with crimson: spines 3, with no centrals: flowers large, purple-crimson, darker at base. N. Mex.
From globose to cylindrical, with depressed vertex, simple or proliferous, 2 1/3-3 3/5 in. broad: ribs 40-55 (sometimes as few as 30), very much crowded and compressed, thin, acute, very wavy, continuous or somewhat interrupted: radial spines 5 (sometimes 6 or 7), straight and spreading, the 2 lowest ones white, rigid, 1/6- 1/4in. long, half as long as the 2 darker, angled, larger laterals, the uppermost spine thin and broad, channeled above, faintly annulate, flexible, grayish pink, 3/5-l in. long; central spines none: flowers small, dirty white. Mex.
bb. Central spine solitary (sometimes 2-4 in E. cris-patus, E. helophorus, and E. setispinus, or wanting in E. lophothele).
c. stems with less than 13 ribs.
Somewhat clavate-cylindri-cal, pale: ribs 8-10, thick, obtuse, strongly tuberculate, the areoles with strong wool: radial spines 7 or 8, similar, straight, finely pubescent, at first yellowish, at length white; central spine solitary, more or less erect, rarely wanting: flowers light yellow. Mex.
Subglobose: ribs 8, broad, compressed, vertical, thickly covered with close-set white woolly spots, making the whole plant almost white: radial spines 7, straight, stout, yellowish or becoming gray; central spine solitary. Mex.
Very large (sometimes as much as 10 ft. high and as much in circumference), globose or oblong, purplish toward the top: ribs 8, obtuse, tuberculate: areoles large, distant, with very copious yellowish wool: radial spines 8 or more; central spine solitary; all the spines shaded yellow and red or brownish, straight, rigid, and interwoven: flowers bright yellow, about 3 in. broad. Mex.
Glaucous, depressed-globose or at length ovate or even cylindric with age, 2-8 in. high, 2 1/2- 4 in. diam.: ribs 8-10 (fewer in very young specimens), often spirally arranged, the tubercles scarcely distinct by inconspicuous transverse grooves: spines 6-9, stout, compressed, reddish (at length ashy), recurved or sometimes almost straight, nearly equal, 4/5-1 1/2 in. long (sometimes long and slender and almost terete, sometimes short, stout and broad); radials 5-8, upper ones weaker, lowest wanting; a single stouter decurved central (sometimes wanting): flowers pale rose-purple, 2 1/2 in. long or more. New Mex. and N. Mex.
cc. stems with 13-27 ribs.