52 THE CACTACEAE. 



short (2 to 6 cm. long) ; areoles on old stems bearing 3 or 4 long (2 to 4 cm. long) needle-like brownish 

 spines; young areoles usually with a single spine each, filled with brown wool; glochids brown, numer- 

 ous sheaths on young spines straw-colored, soon deciduous; flowers and fruit unknown. 



Description based on field notes and on living and herbarium specimens. 



Collected by Dr. Rose on Santa Cruz Island, Gulf of California, April i, 1911 (No. 16845). 



OPUNTIA sp. 



Procumbent, forming an indeterminable mass of spiny branches, 3 to 10 dm. in diameter; old 

 stems woody, smooth, brown, and shiny, 2 cm. in diameter; branches 10 to 20 cm. long, bluish green; 

 spines of two kinds; the 2 to 4 principal ones long (2 to 3 cm. long), needle-like, at first covered with 

 thin yellow sheaths, straw-colored when young, becoming purplish, finally fading to gray; secondary 

 spines 4 to 6, radial, inconspicuous; glochids brownish; flowers and fruit unknown. 



Description based on field notes and living and herbarium specimens. 



Collected by Dr. J. N. Rose on East San Benito Island, off the coast of Lower Cali- 

 fornia, March 9, 1911 (No. 16085). This is, doubtless, the plant referred to by Walton 

 (Cact. Journ. 2: 137. 1899) as 0. ramosissima, but it is not that species. 



Series 3. THURBERIANAE. 



Bushy, arborescent, or depressed species, with slender joints, the ultimate ones tuberculate, 

 about 2 cm. thick or less, the areoles bearing several spines. We recognize 8 species, 7 of them 

 natives of the southwestern United States and northern Mexico, and i in Lower California. 



KEY TO SPECIES. 



Bushy or arborescent species, 6 dm. high or higher. 

 Tubercles narrowly oblong, i cm. long or more. 



Joints readily detached 8.0. vivipara 



Joints not readily detached. 



Longer spines 2.5 cm. long or longer. 



Flowers orange to scarlet 9. 0. letracantha 



Flowers purple 10. O. recondita 



Spines 2 cm. long or less . . . . n. O. llnirberi 



Tubercles low, oblong, 6 to 8 mm. long 12. 0. clavellina 



Depressed species, 6 dm. high or less. 



Spines yellow or brown; flowers green or tinged with yellow. 



Spines yellow, up to 5 cm. long; petals i to 1.5 cm. long . 13. O. darisii 



Spines brown, 2.5 cm. long or less; petals 2 to 2.5 cm. long. . 14. O. viridiflora 



Spines white; flowers yellow 15. 0. whipplei 



8. Opuntia vivipara Rose, Smiths. Misc. Coll. 52: 153. 1908. 



Plant 2 to 3.5 meters high, usually several strong branches from the base, 8 to 10 cm. in diame- 

 ter, much branched above, but not compactly so; old stems with rather smooth bark; young branches 

 bluish green, slender, i to 2 cm. long, 10 to 12 mm. in diameter; tubercles low, oblong, 15 to 20 mm. 

 long; areoles when young bearing a dense cushion of yellow wool with few or no glochids; spines 

 i to 4, 2 cm. long or less, porrect or ascending, covered with straw-colored sheaths ; leaves small, terete, 

 acutish, purple; flowers numerous, borne in clusters at the top of the branches, purplish; ovary 

 strongly tuberculate, bearing white deciduous bristles; fruit oblong, 4 to 6 cm. long, smooth, with a 

 somewhat depressed umbilicus, yellowish green, spineless; seeds white, very thick, 5 mm. long. 



Type locality: Near Tucson, Arizona. 



Distribution: Known only from type locality. 



The relationship of this species is doubtful; it resembles certain garden forms of 

 0. tctracantha, but differs from typical forms of that species in its much larger fruit and 

 seeds, different armament, and habit. The type grew associated with 0. spinosior and 

 0. versicolor, but there is no indication that it is the result of hybridization of those species. 



Illustrations: Smiths. Misc. Coll. 52: pi. 12; Plant World n 10 : f. 12. 



Plate vii, figure 2, represents a branch drawn by L- C. C. Krieger at the Desert 

 Botanical Laboratory, Tucson, Arizona; plate vm, figure i, is from a photograph of 

 the type plant taken by Dr. MacDougal in 1908. 



