578 CACTACEAE 



areolae on the ribs or the tubercles. Flowers arising close above the spine-bear- 

 ing, fully developed areolae, hence appearing lateral on the stem. Hypanthium 

 prolonged beyond the ovary, scaly. Style filiform. Fruit fleshy. Seeds tubercled, 

 endosperm scanty; embryo straight. 



Corolla greenish; ribs of the stem about 13. 1. E. viridiflorus. 



Corolla red or purple; ribs usually less than 13. 

 Ribs of the stem 8-12. 



Flowers scarlet; central spines 2-7. 



Central spines all terete; flowers 4-6 cm. long, yellowish inside. 



2. E. aggregates. 



Lower central spine quadrangular; flowers 8-10 cm. long. 3. E. Roemeri. 

 Flowers purple or violet. 



Central spines 4-5, straight. 4. E. Engelmanni. 



Central spines solitary, bulbous at the base. 



Central spine terete; radials 12-25 mm. long, the lower stouter. 



5. E. Fendleri. 

 Central spine angular; radials 2-5 cm. long, the lateral ones strongest. 



6. E. mojavensis. 

 Ribs of the stem 5-7. 



Central spine present, 8 cm. long, angled and grooved; radials 6-8, strongly 

 angled. 7. E. goniacanthus. 



Central spine wanting; radials 3-59, almost terete. 8. E. paucispinus. 



1. E. viridiflorus Engelm. Stem globose or sometimes oblong-cylindric, 

 2.5-7.5 cm. high; ribs 13, acute; central spines solitary, stout, straight or curved, 

 12-14 mm. long, variegated with purple and white; radial spines 12-18, strict 

 and radiating, 2-6 mm. long; flowers 2.5 cm. wide, greenish brown without, 

 yellowish green within; fruit elliptic, 10-12 mm. long. Plains and hills: Tex. 

 Wyo. N.M. Son. Submont. 



2. E. aggregatus (Engelm.) Rydb. Ovate or subglobose, obtuse, 3.5-7.5 

 cm. high, 3-5 cm. thick, cespitose in hemispheric tufts; ribs 8-11, tubercled; 

 spine slender, straight, terete; radials 8-12, white, 6-12 mm. long, the upper 

 shorter; central spines 1-3, stouter, 1-2 cm. long; flowers deep scarlet, 3.5-6 cm 

 long, 2.5-3.5 cm. broad. Cereus coccineus and C. phoeniceus Engelm. Hillsides 

 and plains: Tex. Colo. Ariz.; n Mex. Son. Submont. 



3. E. Roemeri (Muhlenph.) Engelm. Stem ovoid, 7.5-10 cm. high, spar- 

 ingly branched; ribs 9-11, obtuse, tubercled; spines whitish or straw-colored, 

 with bulbose bases; radials 8-12, slender, straight, the upper 4-10 mm. long, the 

 lateral 12-30 mm. long; central spines 3-5, very bulbose, the lowest quadrangular, 

 dusky when young, 2.5-7.5 cm. long, porrect or reflexed; flowers scarlet, 8-10 

 cm. long, 3.5-5 cm. broad. Cereus Roemeri Muhlenph. C. conioides Engelm. 

 Plains: N.M. Colo. Calif.; n Mex. Son. 



4. E. Engelmanni (Parry) Lem. Stem elliptic-cylindric, 12-30 cm. high, 

 5-7 cm. thick, simple or sparingly branched; ribs 10-12, rarely 13, tuberculate; 

 radial spines 12-14, slender, 6-12 mm. long, white, with dark tips, the upper 

 setaceous and the lower stoutest; central spines 4 (or 5), straight and angled, 

 2.5-5 cm. long, the 3 upper yellow, straight, the lowest white, porrect or reflexed; 

 flower purple, 5-7 cm. long; fruit ovate, 4 X 2.5 cm. Cereus Engelmanni Parry. 

 Deserts: Utah Calif. L. Calif. Sonora. L. Son. 



5. E. Fendleri (Engelm.) Rumpl. Stem ovoid or ovoid-cylindric, 7.5-20 

 cm. high, 5-7.5 cm. in diameter, cespitose; ribs 9-12, tuberculate; radial spines 

 5-10, straight or curved, the lowest stoutest, white and angular, 12-25 mm. long; 

 central spine 1, stout and bulbose at the base, curved upwards, reddish black, 

 2.5-5 cm. long; flowers violet-purple, 6-8.5 cm. broad; fruit ovate-globose, 2.5-3 

 cm. long, purple-green, edible. Cereus Fendleri Engelm. Dry plains: Tex. 

 Utah Ariz.; n Mex. Son. 



6. E. mojavensis (Bigel. & Engelm.) Rumpl. Stem ovate, glaucous, 5-8 

 cm. high, densely tufted, forming masses 1 m. wide; ribs 8-12, slightly tubercled; 

 central spine angular, dusky, curved upwards, 3.5-6 cm. long; radials 5-8, 

 stout, curved, and interlocked, white or with tawny tips, the upper and lower 

 2-3 cm. long, the lateral ones 3-5 cm. long; flowers deep crimson, 5-7 cm. long; 

 fruit oblong, 2.5-3 cm. long. Deserts: Calif. Utah Ariz. Son. 



