OPUNTIA. 193 



The following may be referable to this series : 

 OPUNTIA CRYSTALENIA Griffiths, Bull. Torr. Club 43: 528. 1916. 



Erect, 2 to 2.5 meters high; joints broadly obovate, 25 cm. long, 18 cm. wide, glaucous, bluish 

 green, becoming yellowish in age; leaves 4 mm. long, subulate; spines white, porrect, only on the 

 upper parts of the joints, i to 4, usually only 2, the longest i to 1.5 cm. long; glochids yellow; flowers 

 yellow; stigma-lobes 10, dark green; fruit subglobose, 4 to 4.5 cm. in diameter. 



Type locality: Cardenas, Mexico. 



Distribution: Highlands of Mexico, where it is also cultivated. 



Series 23. POLYACANTHAE. 



This series is confined chiefly to plains of the western United States. The species arc all low, 

 creeping plants, very spiny, with dry fruits. On account of the dry fruit this series forms a natural 

 group, although some species in the series Basilarcs also have dry fruits. One species of series 

 Polyacanthae has fragile branches, in this respect resembling the Citrassavicac. The species 

 hybridize with those of the Tortispinae. 



KEY TO SPECIES. 



Joints readily detached, turgid, sonic of them subtcrete or subglobose 216. O. fragilis 



Joints not readily detached, usually flat and thin, or in 0. arenaria sometimes turgid and 

 nearly terete. 



Joints turgid, usually small 217. 0. arenaria 



Joints thinner than the last, mostly flat, larger. 



Spines, or some of them, very long, flexible and bristle-like. 



Flowers 4 to 5 cm. long 218. 0. trichophora 



Flowers 5 to 6 cm. long. . 219. 0. crimiccn 



Spines stiff, acicular or subulate; arcoles distant. 

 Spines subulate. 



Fruit naked 220. 0. jnniperina 



Fruit spiny. 



Flowers yellow 221. 0. hystricina 



Flowers red 222. 0. rhodantha 



Spines acicular, slender; areoles close together. 



Ovary and fruit without spines 223. O. sphaerocarpa 



Ovary and fruit with spines 224. O. polyacaiitliu 



216. Opuntia fragilis (Nuttall) Haworth, Suppl. PI. Succ. 82. 1819. 



Cactus fragilis Nuttall, Gen. PI. i: 296. 1818. 



Opuntia. brachyarlhra Engelmann and Bigelow, Proc. Amer. Acad. 3: 302. 1856. 



Opuntia fragilis brachyarthra Coulter, Contr. U. S. Nat. Herb. 3: 440. 1896. 



Opuntia fragilis caespitasa and tubcrifortnis Hortus, Stand. Cycl. Hort. Bailey 4: 2363. 1916. 



(?) Opuntia colitmbiana Griffiths, Bull. Torr. Club 43: 523. 1916. 



Usually low and spreading, small and inconspicuous, but sometimes forming mounds 2 dm 

 high in the center and 4 dm. in diameter, with hundreds of joints; joints fragile (the terminal ones 

 especially breaking off at the slightest touch), often nearly globular but sometimes decidedly flat- 

 tened, usually dark green, i to 4 cm. long; areoles closely set, small, filled with white wool; spines 

 5 to 7, brown or only with brown tips and lighter below, i to 3 cm. long; glochids yellowish; flowers 

 pale yellow, about 5 cm. broad; fruit dry, spiny, 1.5 to 2 cm. long, with a truncate or slightly 

 depressed umbilicus; seeds large, 5 to 7 mm. broad. 



Type locality: "From the Mandans to the mountains, in sterile but moist situations." 



Distribution: Wisconsin to central Kansas and northwestern Texas, westward to Ari- 

 zona, Oregon, Washington, and British Columbia. 



Dr. Engelrnann says "it is rarely found in flower and still more rarely seen in fruit." 

 The only fruit we have seen was collected by Dr. Rose near Liberal, Kansas, in 1912. 



Opuntia brachyarthra, sometimes regarded as a variety of O. fragilis, we regard as not 

 specifically separable from that species. An examination of the type material now pre- 

 served in the Missouri Botanical Garden does not warrant a separation of any kind. 



This species is of wide distribution and is especially common on the plains. It usually 

 grows low, often being hidden by the grass. In the grazing country it is a most trouble- 

 some weed, for the joints easily break off and become attached by their spines to passing 

 objects, thus greatly annoying and pestering all animals on the range, even frightening 



