906 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



2. Nyctocereus oaxacensis Britt. & Rose, Cactaceae 2: 120. 1920. 



Oaxaca ; type from Lagunas, at 255 meters. 



Stems branching, slender, 2 to 3 cm. in diameter; ribs 7 to 10, rattier low; 

 areoles 10 mm. apart ; radial spines 8 to 12, 4 to 15 mm. long, slender, brownish ; 

 centrals 3 to 5 ; flowers 8 to 10 cm. long, " whitish inside, dirty purplish or 

 reddish outside " ; perianth segments linear to oblong, rounded at apex ; ovary 

 densely covered with brownish bristly spines. 



15. ACANTHOCEREUS Britt. & Eose, Contr. U. S. Nat. Herb. 12: 432. 1909. 



Weak elongate many-jointed cacti, at first erect but soon clambering or 

 trailing, the joints usually strongly 3-angled, sometimes 4 or 5-angled, in one 

 species sometimes 7-angled, the seedlings and juvenile branches not as strongly 

 angled, with more ribs and with different spines; areoles bearing short wool 

 or felt and several stiff spines; flowers funnelform, nocturnal, 1 at an areole; 

 flower tube remaining rigid after anthesis, gradually drying and remaining 

 on the ripe fruit, green, rather slender, expanded toward the summit, bear- 

 ing a few areoles similar to those of the branches subtended by small scales ; 

 limb somewhat shorter than the tube, widely expanded ; outer perianth seg- 

 ments narrowly lanceolate to linear, acuminate, green, shorter than the 

 white inner segments ; fruit spiny or naked, with a thick, dark red skin break- 

 ing irregularly from top downward ; flesh red ; seeds numerous, black. 



Three other species are known, natives of Central and South America. 



Ribs usually 3, rarely 4, thick. 

 Joints 8 to 10 cm. wide, deeply crenate ; spines very stout, subulate. 



1. A. horridus. 

 Joints 2 to 8 cm. wide, low-crenate ; spines slender. 



Spines well developed, subulate 2. A. pentagonus. 



Spines short or none, when present acicular 3. A. subinermis. 



Ribs 3 to 5, thin 4. A. occidentalis. 



1. Acanthocereus horridus Britt. & Rose, Cactaceae 2: 122. 1920. 

 Oaxaca. Guatemala. 



Plants stout, the joints strongly 3-angled or 3-winged, the young growth 

 5 or 6-angled ; areoles large, 3 to 6 cm. apart ; spines brown or blackish when 

 young ; radial spines 1 to 6, very short, conic, less than 1 cm. long ; central 

 spine usually 1, sometimes 2, often very stout and elongate, sometimes 8 cm. 

 long ; flower IS to 20 cm. long ; tube 4 cm. long, including the funnelform throat 

 12 cm. long ; throat 4 cm. broad at mouth ; outer perianth segments linear, 

 brown or greenish, 6 cm. long ; inner perianth segments 3 to 4 cm. long ; stamens 

 white; fruit 3.5 cm. long, light red, glossy, covered with large areoles bearing 

 white felt; skin thick, finally splitting; pulp red. 



2. Acanthocereus pentagonus (L.) Britt. & Rose, Contr. U. S. Nat. Herb. 



12: 432. 1909. 

 Cactus pentagonus L. Sp. PI. 467, 1753. 

 Cactus pitajaya Jacq. Enum. PI. Carib. 23. 1761. 

 Cereus pentagonus Haw. Syn. PI. Succ. 180. 1812. 

 Cactus prismaticus Willd. Enum. PL Suppl. 32. 1813. 

 Cereus prismaticus Haw. Suppl. PI. Succ. 77. 1819. 

 Cereus pitajaya DC. Prodr. 3: 466. 1828. 

 Wereus undulatus DC. Prodr. 3 : 467. 1828. 

 Cereus acutangulus Otto; Pfeiff. Enum. Cact. 107. 1837. 



