CACTACEAE (CACTUS FAMILY) 329 



the rest, about size and character of the central, which is solitary, very stout, 

 6 or 7-angled and deeply furrowed, often flexuous, 3-6 cm. long, 2 mm. broad: 

 flower scarlet, about 6 cm. long: fruit and seed unknown. Colorado to New 

 Mexico. 



4. Echinocereus Roemeri (Muhlenpf.) Engelm. & Bigel. 1. c 792. Ovate, 

 conoid-acutish at apex, 7.5-10 cm. high, sparingly branched at base: ribs 9-11, 

 obtuse, tuberculate, with areolae 8-12 mm. apart: spines whitish or straw- 

 color, translucent with bulbous base; radials 8-12, slender and rigid, straight- 

 ish, upper 4-10 mm. long, lateral 12-30 mm.; centrals 3-5 (usually 4), very 

 bulbous, upper hardly longer than lateral radials, lowest quadrangular, often 

 dusky when young, 2.5-7.5 cm. long, porrect or deflexed: flower crimson, 8- 

 10 cm. long, 3.5-5 cm. broad: fruit and seed unknown. Cereus conoideus. 

 Colorado, southward, and westward. 



5. Echinocereus aggregatus (Engelm.) Rydb. Bull. Torr. Bot. Club 33: 146. 

 1906. Ovate or subglobose, obtuse, 3.5-7.5 cm. in height, 3-5 cm. in diameter, 

 caespitose (mostly in dense hemispherical masses 30-100 cm. in diameter): 

 ribs 8-11, tuberculate, with areolae 6-8 mm. apart: spines slender, almost 

 setaceous, straight, terete; radials 8-12, white, 6-12 mm. long, upper much 

 the shorter; centrals 1-3, a little stouter, white or horny, 10-20 mm. long: flower 

 deep crimson, 3.5-6 cm. long, 2.5-3.5 cm. broad: fruit and seed unknown. 

 Cereus phoeniceus. Colorado to New Mexico and Arizona. 



4. OPUNTIA Mill. 



Articulated, much branched plants of various shapes, low and prostrate or 

 erect and shrub-like, with young branches bearing small, terete, subulate, early 

 deciduous leaves and in their axils an areohi with numerous short, easily de- 

 tached barbed bristles and (usually) stouter spines. Flowers mostly large, 

 diurnal, with very short cup-shaped tubes on joints of the previous year and 

 on the same areolae with the spines. Petals widely spreading. Ovary with 

 bristle-bearing areolae in the axils of small, terete, deciduous leaves. Fruit a 

 succulent or dry berry marked with bristly or spiny areolae. 



Joints short and flat (except in Nos. 8 and 9). 

 Internodes oval or orbicular. 



Fruit pulpy, unarmed or nearly so. 



Spines dissimilar in size, 1-3, or wanting . . . 1. O. humifusa. 



Spines similar, 1-8. 

 Spines not twisted. 



Spines 1-3; internodes suborbicular . . . 2. O. camanchica. 



Spines 5-7; internodes oblong 3. O. Schweriniana. 



Spines twisted; internodes suborbicular .... 4. O. tortispina. 

 Fruit dry and more or less spiny. 



Corolla yellow 5. O. polyacantha. 



Corolla red. 



Fruit nearly unarmed; filaments yellow . . . 6. O. xanthostemma. 



Fruit very prickly; filaments red . . . . 7. O. rhodantha. 



Internode.s flattened or subterete, the stem readily disjointing. 



Flowers yellowish 8. O. fragilis. 



Flowers pink or reddish . . . . . . 9. O. rutila. 



Joints long, subcylindric. 



An erect tree-like shrub 10. O. arborescens. 



Spreading or procumbent, freely branched . . . . 11. O. Davisii. 



1. Opuntia humifusa Raf. Med. Bot. 2: 247. 1830. Diffuse, from a fibrous 

 root, with obovate or suborbicular, very green joints 7.5-12.5 cm. long, bearing 

 elongated, subulate, spreading leaves 6-8 mm. long: pulvini 1.8-2.5 cm. 

 apart, with slender, reddish-brown bristles, mostly unarmed: spines (when 

 present) few, mostly only marginal, stout, terete, straight, erect or spreading, 

 whitish (often reddish at base and apex), 1.8-2.5 cm. long, single, or 1 or 

 2 smaller deflexed ones in addition: flowers sulphur-yellow (often with red 

 center), 6-S.5 cm. broad: fruit clavate, naked, with funnel-shaped umbilicus. 

 3.5-5 cm. long (less than half that in diameter), with acid or sweetish purplish 

 pulp: seeds almost regular, compressed, with rather narrow and thick but 

 acutish margins, 5 mm. broad. O. Rafinesquii. In the Mississippi valley, 

 and on the eastern base of the Rocky Mountains. 



