GENUS 4. 



CACTUS FAMILY. 



573 



4. Opuntia polyacantha Haw. Many-spined Opuntia. Tuna. Fig. 2990. 



Cactus ferox Nutt. Gen. i: 296. 1818. Not 

 Willd. 1813. 



Opuntia polyacantha Haw. Syn. PI. Succ. 

 Suppl. 82. 1819. 



Opuntia missounensis JJC. Prodr. 3 : 472. 1828. 



Prostrate, joints broadly obovate to or- 

 bicular, tubercled, pale gree: , 2'-6' long, 

 about 6" thick, the tubercles 2' high, 

 densely spiny and with cushions of fine 

 bristles; spines 5-12, slender, 6"-2' long, 

 whitish ; leaves minute ; flowers light yel- 

 low, 2 '-3' broad; fruit dry, very prickly, 

 i'-ii' long. 



Plains and dry soil, Wisconsin to South Da- 

 kota, Athabasca, British Columbia, Nebraska, 

 Missouri, Utah and New Mexico. May-June. 



6. Opuntia fragilis (Nutt.) Haw. Brittle 

 Opuntia. Tuna. Fig. 2991. 



Cactus fragilis Nutt. Gen. i : 296. 1818. 



Opuntia fragilis Haw. Syn. PI. Succ. Suppl. 82. 1819. 



Decumbent or prostrate; joints ovoid, i'-2' long, 

 somewhat flattened or nearly terete. Leaves very 

 small, reddish ; cushions composed of few bristles ; 

 central spines 1-4, i'-ii' long, gray, darker at the 

 apex, surrounded by 4-6 smaller ones ; flowers yel- 

 low, smaller than those of the preceding species ; 

 fruit nearly i' long, becoming dry at maturity, pro- 

 vided with cushions of bristles usually bearing a few 

 short spines. 



Prairies and dry soil, Iowa, Wisconsin and Minnesota 

 to South Dakota, British Columbia, Kansas and Utah. 

 July-Sept. 



7. Opuntia arborescens Engelm. Tree-cactus. 

 Fig. 2992. 



Opuntia arborescens Engelm. Wisliz. Rep. 6. 1848. 



Erect, tree-like, 4-25 high, 4'-8' in diameter at the 

 base, verticillately branched, the spiny branches spread- 

 ing or drooping. Joints verticillate, mostly in 3's or 

 4*s, cylindric, 2'-6' long, less than i' in diameter, the 

 prominent tubercles 7"-io" long; leaves terete, spread- 

 ing, 6"-io" long; spines 8-30, terete, in yellowish 

 sheaths, diverging, the interior ones the longer, often 

 i' long or more; flowers purple, 2^-3' broad; fruit 

 subglobose, crested-tuberculate, dry, or nearly so, yel- 

 low, unarmed, about i' in diameter; seeds smooth, 

 i* "-2" wide. 



Western Kansas, probably only in cultivation ; Colorado 

 to Texas, New Mexico, Arizona and Mexico. 



