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OPUNTIA. 



137 



Key to Species. 



Joints elongated ,32. 0. mcgarhiza 



Joints obovate to orbicular. 



Fruit small, 2 cm. long or less 133. 0. hallii 



Fruit large 2.5 to 6 cm. long. 



Flowers red to purple 134. O. pottsii 



Flowers yellow. 



Areoles large, more or less elevated on old joints; joints glaucous, purplish about the 



areoles .^ 135, 0, setispina 



Areoles small; mature joints green throughout. 



Joints usually orbicular; seeds 5 to 6 mm. broad 136. 0. mackensenii 



\ Joints obovate; seeds 4 mm. broad or less 137. 0. tcnuispina 



132. Opuntia megarhiza Rose, Contr. U. S. Nat, Herb. 10: 126. 1906. 



Roots long and thickened, sometimes 3 to 6 dm. long, 5 to 6 cm. in diameter; stems low, 2 to 

 3 dm. high, much branched; lower joints elongated, 2 to 3 dm. long, cuneate below, thin, 3 cm. 

 broad; lateral joints appearing along the margins of the older joints and often, if not always, in the 

 same plane; spines 2 to 4, acicular, i to 2.5 cm. long, brown; leaves minute; flowers lemon-yellow, 

 often tinged with rose, 5 cm. broad; petals about 13, obovate, mucronately tipped; stigma-lobes 7, 

 greenish; ovary clavate, 3 cm. long; fruit and seeds unknown. 



Type locality: Alvarez, Mexico. 

 Distribution: San Luis Potosi, Mexico. 

 I This species is not very closely related to the 



other species of this series, but it is referred here on 

 account of its very slender spines. 



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133. Opuntia ballii Rose, Contr. U. S. Nat. Herb. 13: 309- 

 A 1911. 



Plants low, spreading; joints obovate, 6 to lo cm. long, W 

 thickish, pale green, glaucous; spines 2 to 4, brownish, a little A ^ 

 flattened, usually ascending or erect, the larger ones 4 to 7 cm. 

 long; glochids conspicuous; fruit small, about 2 cm. long, 



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f -^ clavate, glaucous, spineless; seeds thick, 3.5 mm. broad. 



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Type locality: Pecos, Reeves County, Texas. Fio. i 72.-0. baiiii. Part of type. xo.5. 



Distributiojt: Western 



Wooton and Standlev in their Flora of New Mexico refer this species to Opuntia fil 



pendula 



stouter and erect 



mesa 



Illustrations: Contr. U. S. Nat. Herb 

 Figure 172 is cooied from the illustra 



134. Opuntia pottsii Salm-Dyck, Cact. Hort. Dyck. 1849. 236. 1850. 



Opuntia filipendula Engelmanii, Proc. Amer. Acad. 3: 294- J856. 



Low, spreading plant. 3 dm. high or less, from thickened tuberous roots ^ f 3 cm in diamete^ 



these sometimes moniliform; joints broadly obovate, 3-5 to 12 cm. ^^"f ' P^^f ^^^ ^^^^^^^ 



few either small or lar^e- soines confined to the upper and margmal areoles, i or 2, slender, 2 to 



lew, eitner small or large spmes ^""'"'^ ,. , f/lt^j^g yellow, usually few but sometimes abun- 



4 cm. long, usually white but sometimes purplish, giocnias yeuuvv, u y 



dant; flowers large. 6 to 7 cm. broad, deep purple; ovary slender, 3 to 3.5 cm. long. vMth only 



scattered areoles; fruit spineless. 



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^' Type locality: Near Chihuahua City, Mexico. , ^. , c -^ 



' T<L.:u..,^J. r^o„f.ol rh\hn^hn^. Mexico, to Texas and New Mexico 



Di 

 This 



Salm-Dyck in 1850 from 



John Potts, who was manager of the mint 



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