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140 



THE CACTACKAE. 



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Key to Species. 



More or less bushy plants. 



Joints thin; spines, when present, very long and confined to the upper and middle areoles. 



Spines dark brown, stout, rigid. 



Plant pale green to purplish; spines up to 12 cm. long .' . . 138. O. macrocentra 



Plant dull dark green; spines 6 cm. long or less i39- O. tardospina 



Spines pale brown, flexible or subulate. 



Usually abundantly spiny 140- O. gosseliniana 



Usually spineless or some areoles with i setaceous deflexed spine 141. O. santa-rita 



Joints thick; spines not confined to the upper and middle areoles. 



Joints relatively small, seldom over 15 cm. broad; plants relatively low. 



Joints narrowly obovate, about twice as long as ^ide 142. 0. angustata 



Joints broadly obovate to orbicular. ^ " 



Flowers yellow. 



Spines subulate, brown at least in part. ^ 



Plant light green 143- O. atrispina 



Plant bluish green or grayish green. 



Plant erect, 2 meters high or less 144. O. azurea 



Plant bushy, rarely over i meter high 145. O. phaeacantha 



Plant prostrate : 146. O. mojavensis 



Spines acicular, nearly white '. . . 147- O. covillei 



Flowers magenta 148, O. vaseyi 



Joints relatively large, mostly over 15 cm. broad; plants relatively tall. 



Spines clear brown nearly throughout 149. O. occidentalis 



Spines nearly white above or throughout. 



Spines with dark brown bases 150. O. engelmannii 



Spines whitish throughout 151. O. discaia 



Small creeping plants 152. O. rastrera 



138. Opuntia macrocentra Kn- 



gelmann, Proc. Amer. 

 Acad, 3: 292, 1856. 



Somewhat bushy, with as- 

 cending branches, 6 to 9 dm. 

 high; joints orbicular to oblong, 

 or sometimes broader than long, 

 10 to 20 cm. long, often bluish 

 or purplish, sometimes spineless 



but usually bearing spines at the ^'*^>^ \ T /" ^ 



uppermost areoles ; spines i or2, 



rarely 3 together, usually brown- X X X/l ^ 



ish or black but sometimes white x^^ \J^ 3 



above, slender, erect or porrect, >. / ^ '^ 



4 to 7 cm. long; flowers yellow, ^>(? G 



often drying red, 7.5 cm. broad; ' ^ 



sepals ovate, acuminate; ovary f ^ ^ ^ '^ 



with few areoles, these bearing p 



brown glochids; filaments very I ^ ' ^ 



short; fruit 3 to 6 cm. long, pur- 'A % ^ 



pie; seeds 4 to 4.5 mm. broad. \ ^ « » 



Type locality: Sand hills "Xi ^ ^ ^ 



on the Rio Grande near El \ * ^ 



Paso, Texas. V'' ^ ^ ^ 



Distribution : Western \ 9 ^ 



Texas to Eastern Arizona ' \ ^ ^ 



and Chihuahua, Mexico. ^t ^ 



This species, especially \ ^~ 



the forms that have bluish ) , 



and purplish joints, are very y » 



showy. Seedlings sometimes >fe © 



produce long, silky hairs from 



the areoles, in this respect '*^'' 



resembhng the Criniferae. Pir ,-,« n .• 



° •' 1*10.176. — Opuntia macrocentra. X0.5. 



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