20 8 CACTUS ORDER 



Stems with nipples 



1. Stems with nipples 



a. Central spines 8-10; radial spines 20-30; flow- 



ers greenish-yellow to purple E. Simpsoni 



b. Central spines 1-3 ; radial spines 8-9 ; flowers 



rose E. glaucus 



2. Stems with ribs or ridges ; central spines 4 ; radial 



"spines 9-11; flowers yellow E. Whipplei 



ECHINQCEREUS ENGELMANN 1848 



(Gr. e chinos, hedge hog, Cereus, a genus of cacti) 



Sepals many, united into a tube grown to the ovary, petals many, 

 purple, red to yellowish-green, fruit spiny ; flowers borne on the ribs or 

 tubercles, close to fully developed clusters of spines; stems ovoid, cylindric 

 or oval, ribbed, the ribs somewhat tubercled. 



1. Ribs usually 13; flowers greenish-yellow E.viridifloTus 



2. Ribs 5-12 ; flowers red to purple 



a. Ribs 5-7; flowers red 



(1) Radial spines 3-5, nearly round; central 



spine absent E. paucispinus 



(2) Radial spines 6-8, angled; central spine 3- 



8 cm. long . E. gonacdnthus 



b. Ribs 8-12 



(1) Central spine 1, black; radial spines usual- 



ly 7 ; flowers violet-purple E. Fendleri 



(2) Central spines 1-3, white or yellowish ; 



radial spines 8-12 ; flowers red E. aggre gatus 



OPUNTIA Miller 1759 PRICKLY PEAR 



(Gr. name of a plant) 



PL 32, fig. 6. 



Sepals many, united into a tube grown to the ovary, petals many, yel- 

 low, red or purple, slightly united at base, stamens very numerous in several 

 rows, berry pear-shaped, smooth or spiny ; flowers usually somewhat lateral ; 

 stems jointed, branching, the joints flat or cylindric with small, awl-shaped, 

 deciduous leaves, the areoles axillary, usually spine-bearing. 

 1. Joints of the stem flat, oval to round 



a. Fruits fleshy, smooth or nearly so ; flowers yel- 

 low 

 (1) Spines none or a single large reflexed one 



and 1-2 small ones 0. humifusa 



