ACANTHOCEREUS. 



121 



Stems 6 to 10 dm. high; branches numerous, radiating and ascending, 3 to 5 cm. in diameter, 

 entirely covered by a mass of yellow spines; ribs about 20, low, 3 mm. high; areoles 5 to 6 mm. 

 apart; spines about 40, unequal, the longer ones about 3 cm. long, bristle-like; flower 7 cm. long; 

 outer perianth-segments 1.5 cm. long, 2 mm. broad; inner perianth-segments longer than the outer, 

 narrow; filaments i mm. long or less; fruit 2.5 to 4 cm. long, 1.3 cm. in diameter; se^eds numerous, 

 1.2 mm. long, ellipsoid, brownish, slightly punctate. 



Type locality: Charles Island, Galapagos. 



Distribution: Albemarle, Abingdon, Chatham, James, Charles, and Tower Islands, 

 Galapagos. 



We have identified Cereus thouarsii Weber, by photographs of the specimens sent by 

 Professor Agassiz to Dr. Engelmann, preserved at the Missouri Botanical Garden, and 

 mentioned by Dr. Weber at the place of first publication. 



Schumann says this species is a very peculiar one, 

 "from its long, brown, non-pungent spines, which clothe 

 the stem so densely that its surface is invisible. I have 

 never before seen a species of the genus with such short fila- 

 ments as in this. The petals are also uncommonly narrow." 



Berger refers this species to his subsection Nyctoccrcns, 

 with which it is probably most nearly related. It was 

 named for Abel Aubert Du Petit-Thouars (1793-1864). 



Illustration: Proc. Calif. Acacl. Sci. IV. i: pi. 5, as 

 Cereus nesioticus. 



Figure 179 shows the flower of the type specimen of 

 Cereus nesioticus preserved in the Gray Herbarium; figure 

 180 shows the fruit of Bracliyccrcus tliouarsii collected 

 by A. vStewart, preserved in the herbarium of the Cal- 

 ifornia Academy of Sciences. 



Fir,. i7<j. Flower 

 of B. thouarsii. 

 Xo.8. 



FIG. 180. Fruit 

 of same species. 

 Xo.8. 



22. ACANTHOCEREUS (Berger) Britton and Rose, Contr. U. S. Nat. Herb. 12: 432. 1909. 



Weak, elongated, 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 y-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, i at an areole; 

 flower-tube remaining rigid after anthesis, gradually drying and remaining on the ripe fruit, green, 

 rather slender, expanded toward the summit, bearing a few areoles similar to those of the branches, 

 subtended by small scales; limb somewhat shorter than the tube, widely expanded; outer perianth- 

 segments narrowly lanceolate to linear, acuminate, green, shorter than the white, inner segments; 

 stamens not extending as far as perianth-segments, attached all along the upper half of the tube 

 or throat; style very slender, divided at the apex into several linear stigma-lobes; fruit spiny or naked, 

 with a thick, dark-red skin breaking irregularly from top downward; flesh red; seeds numerous, black. 



This genus has a wide distribution; its species are usually found at low altitudes in 

 semiarid regions, especially about the Gulf of Mexico and the Caribbean Sea; although 

 occurring on the coasts of Texas and Florida and recorded from Cuba, it has not been 

 reported from any of the other larger Antilles, but is represented on the Venezuelan and 

 Colombian coasts and also in Central America and Brazil. It is found not only on the 

 east and west coasts of Mexico but also in the interior. 



The type of this genus is based on the Cactus pentagon its of Linnaeus. Linnaeus in his 

 Species Plantarum cites no definite habitat for it, while his description is very meager. His 

 earlier reference in Hortus Cliffortianus (182. 1737), although somewhat fuller, is still 

 uncertain. It is there stated that the ribs are 5, sometimes 6. Most of the species of this 

 genus, especially those which would have been known in Linnaeus's time, usually have 3 

 ribs, occasionally 4, rarely 5. The young plants and the young growth, however, often 

 have 5 and 6 ribs, which would account for variations in descriptions of the same species. 



