4 THE CACTACEAE. 



KEY TO SPECIES. 



A. Flowers large, 10 to 20 cm. long. 



B. Species tall, columnar (except C. pachyrhiaus), the joints very thick. 

 Ribs 4 to 6, very high, flat or nearly so (Series I. Hexagon<ie\. 

 Young joints glaucous, blue or bluish green. 

 Spines of young joints short or none. 



Ribs usually 4; young joints light blue I. C. hexagonus 



Ribs usually 6; young joints dark blue 2. C. luldinatinianus 



All joints manifestly spiny. 



Young spines bright yellow 3. C. alacriportanus 



Young spines not yellow. 



Flowers red without 4. C. ralidits 



Flowers green without 5. C. janiacuru 



Young joints not glaucous, green, or sometimes glaucous in No. 7. 



Inner perianth-segments red 6. C. tetragonus 



Inner perianth-segments white (unknown in C. xanthocarpus). 

 Outer perianth-segments red. 



Spines i to 3, short or wanting or elongated in No. 7; seeds dull. 



Berry red or orange, unpleasant to the taste 7. C. slenognnus 



Berry yellow, edible 8. C. xanthocarpus 



Spines 8 to 13, up to 4 cm. long; seeds shining. 



Tree-like, 6 to 8 meters high, not densely spiny 9. C. lamprospermus 



Lower, i to 3 meters high, densely spiny 10. C. paehyrhizus 



Outer perianth-segments green or brownish. 



Spines few, short or wanting n. C. dayamii 



Spines 6 to 10, up to 10 cm. long 12. C. argeiitinensis 



Ribs 6 to 9, rarely 4, thicker and lower; outer perianth-segments brownish 



(Series 2. Peruvianae) 13. C. peruvianus 



BB. Species lower, prostrate, or bushy, the joints mostly not as stout (C. clialybaeus tall). 

 Joints green (Series 3. Obtusae). 



Ribs only 4 to 6 mm. high; plants shining 14. C. perhicens 



Ribs much higher; plants dull. 



Spines subulate 15. C. variabilis 



Flower 20 to 24 cm. long. 



Flower 12 to 16 cm. long 16. C. pernambucensis 



Spines acicular. 



Radial spines 5 to 7; central spine i 17. C. obtusus 



Radial spines 8 to 10; central spines 4 to 7 18. C. caesius 



Joints glaucous blue; species slender (Series 4. Azureae). 



Ribs strongly sinuate 19. C. azitreus 



Ribs not strongly sinuate. 



Tree-like; areoles distant 20. C. clialybaeus 



Bush-like; areoles close together 21. C. aclhiops 



AA. Flowers small, 8 cm. long or less; plants columnar (Series 5. Repandae). 

 Flowers 7 to 8 cm. long; spines straight, acicular. 



, Spines up to 5 cm. long, acicular; flowers green; branches constricted 22. C. rrpaiidus 



Spines 2 cm. long or less; flowers purple; branches continuous 23. C. grenadensi>. 



Flowers 5 to 6 cm. long; spines curved, subulate 24. C. margaritensis 



1. Cereus hexagonus (Linnaeus) Miller, Gard. Diet. ed. 8. No. i. 1768. 



Cactus hexagonus Linnaeus, Sp. PI. 466. 1753. 



Cactus octogonus Page in Steudel, Nom. ed. 2. i: 246. 1840. 



Cereus northumberlandianus* Lambert in Loudon, Gard. Mag. 17: 91. 1841 (February). 



Cereus perrottetianus Lemaire, Icon. Cact. pi. 8. 1841 to 1847. 



Cereus lepidotus Salm-Dyck, Cact. Hort. Dyck. 1849. 207. 1850. 



Plant up to 15 meters high, usually branching near the base, with a trunk 4 dm. in diameter; 

 branches usually strict and erect, but in old plants more spreading, made up of short joints 12 cm. 

 in diameter or more, glaucescent or light green, usually 6-angled but sometimes only 4 or 5-angled, 

 occasionally 7; ribs thin, 3 to 5 cm. high, the margins undulate; areoles about 2 cm. apart, small, 

 felted ; spines on young branches wanting or few, very short (2 to 3 mm. long) , but on old branches 

 often 8 to 10 or perhaps more in a cluster, very unequal, the longest ones 5 to 6 cm. long, when 

 young brown, but lighter in age; flower 20 to 25 cm. long, its tube slender, 10 cm. long; uppermost 

 scales green, short; outer perianth-segments lanceolate to oblong-lanceolate, 6 to 7 cm. long, short- 

 apiculate, tinged with purple; inner perianth-segments much thinner than the outer ones, white, 



*The name was published in Loudon 's Gardener's Magazine first as Cere us norlhumberlandia with a suggestion 

 by the editor that Cereus narthiimberlandianus was the preferred spelling but later in the same year (Hort. Univ. 2: 

 318. 1841) Cereus northumberlandianus was adopted. A re-examination of the description of Linnaeus's Cactus 

 hexagonus, which came from Surinam, leads us to believe that it is the same species and as the name is older than 

 cither C. northumberlandianus or C. lepidotus we here use it. 



