RATHBUNIA. 



169 



The name Pilocereus acranthus was proposed by vSchumann (see plate 5 B of Engler and 

 Drude, Veg. Erde 12: 1911), but was never published. 



Illustration: Engler and Drude, Veg. Erde 12: pi. 5 B, as Pilocereus acranthus. 



Figure 237 is from a photograph taken by Dr. Rose at the type locality in 1914; 

 figure 239 shows the flower, and figure 240 the fruit of the plants photographed. 



30. RATHBUNIA Britton and Rose, Contr. U. S. Nat. Herb. 12: 414. 1909. 



Rather slender cacti, simple or bushy, the stems and branches weak, erect or bent ; ribs few, 4 

 to 8, prominent; spines subulate, those of the flowering areoles not differing from the others; flowers 

 diurnal, scarlet, solitary, usually at the upper areoles, narrowly tubular, the tube bearing distant 

 long scales and united with it except at the tip, elongated, at first straight, or in age somewhat 

 curved, the limb more or less oblique; perianth-segments short, spreading or reflexed; filaments 

 exserted ; style slender, exserted beyond the tube ; stigma-lobes narrow ; ovary with small scales bearing 

 short felt and sometimes spines in their axils; fruit capped by the withered flower, spiny or becoming 

 smooth, globular; seeds of the typical species black, compressed, minutely pitted, with a large basal 

 oblique hilum. 



This genus commemorates Dr. Richard Rathbun (1852-1918), Assistant Secretary of 

 the Smithsonian Institution in charge of the United States National Museum, a well-known 

 authority on marine invertebrates. 



Type species : Ctreus sonorensis Runge. 



We here include 2 species, natives of western Mexico. 



KEY TO SPECIES. 



Ribs 5 to S; flowers 4 to 10 cm. long i. R. alamosensis 



Ribs 4; flowers 12 cm. long 2. R. kerberi 



1. Rathbunia alamosensis (Coulter) Britton and Rose, Contr. U. S. Nat. Herb. 12: 415. 1909. 



Cereus alamosensis Coulter, Contr. U. S. Nat. Herb. 3:406. 1896. 

 Cereus sonorensis Runge in Schumann, Monatsschr. Kakteenk. n: 135. 1901. 

 Rathbunia sonorensis Britton and Rose, Contr. U. S. Nat. Herb. 12: 415. 1909. 

 Cereus pseudosonorensis Gurke, Monatsschr. Kakteenk. 20: 147. 1910. 



Columnar, 2 to 3 meters high, at first erect but generally finally bent or curved, 8 cm. thick or 

 less, rooting at or near the tip and thus forming new plants; ribs 5 to 8, obtuse; radial spines about 

 1 1 to 18, spreading, straight, whitish; centrals i to 4, much stouter than the radials, 3 to 5 cm. long, 

 porrect or ascending; flowers scarlet, 4 to 10 cm. long; scales on ovary small, acute or obtuse, with a 

 small tuft of felt and a few bristle-like spines in the axils, those on the flower-tube with a tuft of 

 felt and sometimes with a spine; tube-proper 1.5 cm. long; style 

 nearly white ; stigma-lobes 6, cream-colored ; ovary tuberculate ; fruit 

 red, globular, 3 to 4 cm. in diameter, naked or bearing scattered 

 clusters of 5 or 6 white acicular spines. 



Type locality: Near Alamos, Sonora, Mexico. 



Distribution: Southern Sonora, Sinaloa, and Tepic, 

 Mexico. 



The plant grows in large clusters sometimes 8 meters in 

 diameter; its flowers are various in size, and the perianth- 

 limb is apparently quite variable in the degree of obliquity. 

 In Mexico the plant is called cina. 



Cereus simonii Hildmann (Monatsschr. Kakteenk. 5: 43. 

 1895), an unpublished name, according to Schumann and 

 Gurke, belongs here. vSchumann at one time described this 

 plant as Cereus stellatus, a very different plant from 

 southern Mexico which we have described elsewhere as 

 Lemaireocereus stellatus (see page 92, ante). 



Illustrations: Bliihende Kakteen 3: pi. 122; Monatsschr.' Kakteenk. 11:135; Rep. 

 Mo. Bot. Card. i6:pl. 3, f. 5, all as Cereus sonorensis; Schumann, Gesamtb. Kakteen 

 Nachtr. f. 4, as Cereus stellatus. 



FIG. 241. Flower of Rathbunia ala- 

 mosensis. Xo.y. 



FIG. 242. Flower of same, cut open. 

 Xo.7. 



