15. ctenoides, Lem. (Cereus ctenmdes, Engelm.). stems solitary or rarely branching, cylindrical to elongated ovoid, reaching a height of 6 in. and a diam. of 2 1/2 in.: ribs 15-16, usually straight: radial spines 13-22, horizontally radiate, pectinate, subulate, bases bulbose and laterally compressed, stiff, straight or often slightly curved, the laterals longest and about 3/8in., the upper ones very short, white or sometimes with brownish tips; centrals 2-3 or rarely 4, superposed, coarser, bulbose at the base, short and conical to 1/4in. long, reddish; later all the spines are gray: flowers lateral, from near the crown, 2 1/2-3 in. long; ovary and short tube white bristly; corolla yellow, with greenish throat. Texas, and N. Mex. - This species is very rare in cultivation

ff. Color of flowers purple.

G. The spines irregularly pectinate.

16. Roetteri, Rumpl

(Cereus Roetteri, Engelm.). Loosely open clustered: stems upright, 4-6 in. high, 2-3 in. diam., cylindrical or ovoid: ribs 10-13, straight: radial spines 8-15, subulate, thickened at the base, stiff, sharp, straight or slightly curved, the laterals longest, about 1/2in., the upper ones shortest, reddish with darker tips; centrals 2-5, stouter, bulbose at base, 1/4-3/8in. long, the lower ones the longest; later all the spines are gray: flowers lateral, from near the crown, 2 1/2-3 in. long, purple-red to violet: fruit short ellipsoidal, spiny, green, 3/4in. long. Texas to Ariz, and N. Mex.

gg. The spines regularly pectinate.

H. Tube of flower and spines of ovary slender and weak, the surrounding hairs long and cobwebby.

17. caespitosus, K. Sch. (Cereus caespitosus, Engelm.). Radials 20-30, curved, clear white or with rose-red tips; centrals absent, or 1-2 very short ones. Okla., Texas and Mex.

hh. Tube of flower and spines of ovary short and stout, the surrounding hairs short.

1. Central spines several.

18. Pectinatus, Engelm

(Cereus pectinatus, Engelm.). Clustered stems cylindrical or ovoid, reaching a height of 10 in. by 3 in. diam.: ribs 13-23, straight: radial spines 16-30, pectinate, horizontally spreading and appressed, straight or curved, the laterals longest, round, hardly 3/8in. long; central usually absent, or as many as 5, which are short, conical and superposed, white, with tips and bases variously colored with pink, yellow or brown; later all become gray: flowers lateral, from near the crown, 2 1/2-4 in. long; ovary tuberculate and spiny, light to dark rose-red or rarely white: fruit globose, spiny, green to reddish green. Mex.

Variety adustus, K. Sch. (Cereus adustus, Engelm.). Like the type, but with black-brown to chestnut-brown spines. Mex.

Variety rufispinus, K. Sch. Of more robust growth: radial spines curved, red. Mex.

11. Central spines none.

19. Rigidissimus, Engelm

(Cereus candicans, Hort. C. rigidissimus, Hort.). Rainbow Cactus. Fig. 1376. stems comparatively snorter and thicker: radial spines 16-20, coarser and stiffer, straight or very little curved; base thickened, white, yellow or red to brown, these colors commonly arranged in alternating bands around the plant, the spines of adjacent clusters interlocking; centrals absent. Ariz, and N. Mex.

Echinocereus rigidissimus.

Fig. 1376. Echinocereus rigidissimus.

dd. Spines not pectinate.

E. Ribs 10 or fewer.

f. Flowers crimson.

20. Mojavensis, Rumpl

(Cereus mojavensis, Engelm. & Bigel.). stems clustered, ovoid, reaching 3 in. height by 2 in. diam.: ribs 8-12, conspicuously undulate: radial spines 5-8, the lowest pair the longest, reaching about 2 1/4 in. long; all are white with brown tips, subulate, straight or curved, strongly bulbose at the base; central solitary, or sometimes absent, stronger and somewhat longer and darker colored; later all the spines become gray: flowers 2-3 in. long, deep carmine: fruit ellipsoidal, about 1 in. long. Deserts of Ariz., Nev. and Calif.

ff. Flowers purple-violet.

G. The spines dark, often of several colors.

h. Central spine 1.

21. Fendleri, Rumpl

(Cereus Fendleri, Engelm.). Irregularly clustered: stem cylindrical or rarely ovoid or even globose, sparingly branching, 3-7 in. high by 1 3/4-2 1/2 in. diam.: ribs 9-12, straight or slightly spiral, undulate: radial spines 7-10, subulate, straight or curved, the lowest or the 2 lower laterals the longest, about 1 in., stronger, quadrangular, white; the 2 next higher brownish; the upper ones round, white and much shorter; all are bulbose at the base; central solitary (or in old plants 3-4), very strongly thickened at the base, round, black, sometimes with a lighter colored tip, curved upward, reaching a length of 1 3/4 in.: flowers lateral, from near the crown, 2-3 1/2 in. long, dark carmine-red to purple and violet: fruit ellipsoidal, spiny, green to purple-red, about 1 in. long. Colo., Utah and south to N. Mex. B.M. 6533.

hh. Central spines several.

22. Engelmannii, Lem. (Cereus Engelmannii, Parry). stems clustered, cylindrical to ovoid, 4-10 in. high, 1 3/4-2\i in. diam., light green: ribs 11-13, undulate: radial spines 11-13, somewhat angled, stiff, sharp, straight or somewhat curved, horizontally spreading, the lowest or lower laterals the longest, about 1/2in., the upper ones the shortest, whitish with brown tips; centrals 4, stiff, straight, angled, stout, the lowest one deflexed, white to dark-colored, reaching a length of 2 1/2. in., the upper ones about half as long, spreading, brown: flowers lateral, from just below the crown, l 3/4-2 1/2in. long, purple-red : fruit ovoid, green to purple-red, spiny, later naked, about 1 in. diam.; pulp purple-red. Calif, to Utah and south into Mex.

Variety chrysocentrus, Engelm. & Bigel. The 3 upper centrals golden yellow, the lowest white. Mojave Desert, Calif.

Variety variegatus, Engelm. & Bigel. The 3 upper centrals curved, horn-colored and mottled with black. Utah, Nev. and Calif.

gg. The spines usually white or straw-colored.

H. Central spines somewhat curved.

23. Dubius, Rumpl

(Cereus dubius, Engelm.). Tolerably thickly clustered: stems branching at the base, cylindrical or elongated ellipsoidal, 4 1/2-7 in. high by 1 1/2-2 1/4 in. diam.: ribs 7-9, undulate: areoles 3/8-5/8 in. apart, round, covered with short curly white wool, later naked: radials 5-8, subulate, horizontally spreading, stiff, round or faintly angled, the lower ones usually the longest, about 1 in. long, the upper ones about half as long, or sometimes absent, transparent white; centrals 1-4, stronger and longer, bulbose at the base, straight or curved, reaches 2 1/2 in. length, the lowest one longest, straight, porrect or deflexed, the upper ones spreading: flowers lateral, 2 in. long, rose-red to violet: fruit spherical, greenish to purple-red, covered with bundles of deciduous spines. Texas and N. Mex.

hh. Central spines straight. I. stems erect, with the spines pale at base.

24. Enneacanthus, Engelm

(Cereus enneacanthus, Engelm.). Freely branching at the base of the stem and thus forming thick, irregular clusters: branches ascending, usually 3-5 in. long by 1 1/2-2 in. diam., green or sometimes reddish: ribs 8-10, straight, often divided by transverse grooves into more or less conspicuous tubercles: areoles 3/8- 5/8in. apart, round, white curly-woolly, soon naked: radial spines 7-12 (mostly 8), horizontally spreading, needle-form, straight, stiff, translucent white, base bulbose, the under one longest, reaching about 1/2in., the upper one very short; central solitary, or seldom with 2 additional upper ones, straight, porrect or deflexed, round or angled, whitish to straw-yellow or darker, 3/8-1 1/2 in. long; later all the spines are gray: flowers lateral, from near the crown or lower, 1 3/4-2 1/2 in. long, red to purplish: fruit spherical, green to red, spiny, 3/4-l in. long. Texas and N. Mex.

ii. stems spreading and flabby, with the spines red at base.

25. Merkeri, Hildmann

stems at first upright, columnar, later reclining and by branching at the base forming clusters, in new growth bright green, later gray to gray-brown and corky: ribs 5-9, undulate to more or less tuberculate: areoles 3/4in. and more apart, round, white velvety, later naked: radial spines 6-9, the upper ones the longest, reaching 1 1/4 in. length, somewhat confluent with the centrals, subulate, spreading, straight; centrals 1-2, stronger, reaching a length of 2 in.; all the spines are white, nearly transparent, with red-tinted bulbose base. N. Mex.

ee. Ribs 11 or 13.

f. Plants in small clusters: central spines sometimes solitary.

26. Conglomerates, Forst

stems clustered, columnar, somewhat tapering above, reaching a height of 1 ft. and 2 in. diam., light green: ribs 12-13, strongly undulate, tubercled above: radial spines 9-10, glossy, spreading, the lower pair the longest, base yellow; centrals 1-4, the lowest straight, porrect, reaching a length of 1 1/2 in. and more, somewhat stronger than the rest. N. Mex.

ff. Plants often 200 in a single mound: centrals never single.

27. Stramineus, Rumpl

(Cereus stramineus, Engelm). Clustered in thick, irregular bunches: stems ovoid to cylindrical, 4-8 in. long, 1 1/2-2 1/2 in. diam.: ribs 11-13: radial spines 7-10 (usually 8), horizontally radiate, straight or slightly curved,-subulate, sharp, round or the long lower ones angled, transparent white, tolerably equal in length, about 1/2-3/4in. or the lower ones sometimes longer and reaching a length of 1 1/2 in.; centrals 3-4, much longer, stronger, twisted, angled, straw-yellow to brownish, when young reddish transparent, the upper ones shortest and spreading upward, the lower ones porrect or depressed: flowers lateral, 2 1/2-3 1/2 in. long, bright purple-red or deep dark red, to scarlet: fruit ellipsoidal, about 1 1/2 in. long, covered with numerous spines, purple-red. Texas to Ariz, and N. Mex.

Horticultural names are: E. paucispina, no doubt a mutilation of paucispinue. - E. polycephalus. - E. sanguineus. - E. Schlenii= E. Scheeri (?). - E. tuberosus, Rumpl. =Wilcoxia. - E. Uehri. -E Uspendkii. C. H. Thomson.

J. N. Rose.†