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 radial^ lowest quadrangular, often 

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

 10 cm long, 3.5-5 cm. broad: fruit and seed unknown. Cereuts 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 em. long, 2.5-3.5 cm. broad: fruit and seed imknown. 

 Cereus pAoentceMS.— Colorado to New Mexico and Arizona. 



4. OPUNTIA MiU. 



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 areola 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. hiunifusa. 

 Spines similar, 1-8. 

 Opines 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. 



Fruitnearly unarmed; filaments yellow .... 6. O. xanthostemma. 



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



Internodes 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 htunif usa 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 era: long, single, or 1 or 

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

 center), 6-8.5 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. 0. Bafinesquii. — In the Mississippi valley, 

 and on the eastern base of the Rocky Mountains. 



