12. Cylindropuntia whipplei (Engelmann & J. M. Bigelow) F. M. Knuth in C. Backeberg and F. M. Knuth, Kaktus-ABC. 124. 1935.
Opuntia whipplei Engelmann & J. M. Bigelow, Proc. Amer. Acad. Arts 3: 307. 1856; Cylindropuntia hualpaensis Backeberg; C. whipplei var. enodis (Peebles) Backeberg; O. whipplei var. enodis Peebles; O. whipplei var. laevior Engelmann
Trees or shrubs, low to upright, sparingly to densely branched, some almost matlike in Arizona, 0.3-0.6(-1.5) m; branchlets whorled to subwhorled. Stem segments firmly attached, green, 3-9(-15) × 0.5-1.5(-2.2) cm; tubercles prominent, short, 0.5-1 cm; areoles oval to obdeltate, 2-6 × 1.5-4 mm; wool pale yellow to white, aging gray. Spines (1-)3-8(-10) spines per areole, in all but basalmost areoles, best developed toward apex, interlacing with spines of adjacent areoles, whitish or pale yellow, pale red-brown, sometimes tipped yellow, of 2 kinds; radial spines slender, flattened basally, deflexed, 5-8 mm, surrounding central spines; central spines usually 4(-6), spreading into a cross, stout, subterete, 2-3.4(-4.5) cm; also 0-2 bristlelike spines; sheaths whitish to pale yellow (rarely golden) throughout or tipped yellow to golden. Glochids in adaxial tuft, yellow, 1-3 mm. Flowers: inner tepals yellow to green-yellow, spatulate, 15-25(-30) mm, apiculate; filaments yellowish or yellow-green; anthers yellow; style white to yellowish; stigma lobes whitish, yellowish, or pale green (rarely pink tinged). Fruits rarely proliferating, yellow to greenish yellow, broadly cylindric to subspheric, 18-30(-35) × 15-22(-32) mm, fleshy, tuberculate, spineless; tubercles subequal or distalmost longest, usually prominent; umbilicus 7-8 mm deep; areoles 36-62. Seeds pale yellow, subcircular to slightly angular in outline, flattened to warped, 3-3.5 × 2.5-3.5 mm, sides smooth or with 1-3 depressions; girdle smooth. 2n = 22, 44.
Flowering late spring-early summer (May-Jul). Desert and plains grasslands, juniper woodlands, oak, pinyon, or pine forests, sagebrush; 900-2300 m; Ariz., Colo., Nev., N.Mex., Utah.
Cylindropuntia whipplei hybridizes with C. acanthocarpa in central Arizona; the hybrids [= C. ×congesta (Griffiths) F. M. Knuth (as species) (D. J. Pinkava 1999)] are compact shrubs with long-tuberculate stem segments 8-12 mm thick, bearing 0-4 erect or deflexed spines per areole, and tuberculate, green to yellowish fruits occasionally bearing one to few spines, and have chromosome number of 2n = 22. In areas of Arizona, Nevada, and Utah, C. whipplei hybridizes with C. echinocarpa, particularly with the low, compact form of C. echinocarpa; the hybrids [= C. ×multigeniculata (Clokey) Backeberg] have spineless to nearly spineless fruits, numerous intergrading spines per stem areole that are not dimorphic, and chromosome number of 2n = 22. Hybrids between C. whipplei and C. imbricata [= C. ×viridiflora (Britton & Rose) F. M. Knuth], which are found in scattered localities in northern New Mexico and northeastern Arizona, have a low, bushy habit, ripe cantaloupe-colored inner tepals, an irregular, monomorphic spine pattern, and a chromosome number of 2n = 22. Cylindropuntia ×media P. V. Heath, from the base of Wolf Creek Pass, Colorado (G. Arp 1973), reportedly has the same putative parentage as the older name C. ×viridiflora; further study of its parentage is warranted. Cylindropuntia whipplei also hybridizes with C. leptocaulis.