in C. Backeberg and F. M. Knuth, Kaktus-ABC, 124. 1935.
Trees or shrubs, sparsely to densely branched, 1–2 (–4) m. Stem segments firmly attached, cylindric, 10–30 (–50) × 2–2.5 (–3) cm; tubercles prominent, narrow to broad, 1.5–4.5 cm; areoles elliptic to subcircular, 4–5.5 × 4–5 mm; wool white or yellowish to tan, aging gray-black. Spines 6–20 (–30+) per areole, often accompanied by 0–5 short bristlelike spines at areole margins, usually in distal areoles; major abaxial spines deflexed to divergent, subterete to flattened; major adaxial spines ascending-divergent, terete, yellow or tan to deep redbrown, aging gray, the central spine longest, 12–30 (–38) mm; sheaths white to grayish with yellow to golden tips, baggy to tight-fitting. Glochids in inconspicuous to small adaxial tuft, yellow to brown, 0.5–2 mm. Flowers: inner tepals bright-yellow to bronze to brick-red, spatulate, 20–30 mm, apiculate-emarginate; filaments red; anthers yellow; style and stigma lobes white to light green. Fruits tan at maturity, obconic to ellipsoid, 15–35 × 15–20 mm, dry, tuberculate, densely to sparsely spiny (rarely spineless), with apical flange above shallow umbilicus; basal tubercles longest; areoles 12–30. Seeds pale-yellow to tan, angular or squarish in outline, warped, 3.5–5 × 3–4.5 mm, sides smooth, each with 2–4 large depressions; girdle smooth.
Ariz., Calif., Nev., Utah, n Mexico
Varieties 4 (4 in the flora).
Cylindropuntia acanthocarpa hybridizes with C. abyssi, C. echinocarpa (= C. ×deserta), C. bigelovii (= C. ×campii), C. leptocaulis (see C. ×tetracantha), C. ×multigeniculata, C. spinosior, C. versicolor, and C. whipplei (= C. congesta). Hybrids of C. acanthocarpa and C. ×multigeniculata are more open in habit, with longer stem segments than C. ×multigeniculata and with reddish filaments like C. acanthocarpa.
|1||Tubercles 2.5-4.5 cm, broad; stem segments gray-green; spines of adjacent areoles not or barely interlaced, 6-11(-14) per areole; fruits bearing few spines or sometimes spineless||Cylindropuntia acanthocarpa var. thornbe|
|1||Tubercles (1-)1.5-2.5(-3) cm, broad to narrow; stem segments green to yellow-green; spines of adjacent areoles interlaced; fruits densely spiny, sometimes burlike||> 2|
|2||Abaxial 5-7 spines deflexed, usually subparallel, whitish to light brown; tubercles broad, oval; shrubs with few, ascending branches||Cylindropuntia acanthocarpa var. acantho|
|2||Abaxial (14-)18-30+ spines deflexed to divergent, spreading, pale yellow to red-brown; tubercles narrowly elliptic; shrubs with few to many, spreading branches||> 3|
|3||Branches usually at acute angles; stem segments yellowish green, usually long, commonly 15-30 cm; spines 18-30+, yellow to tan, sheaths baggy; inner tepals yellow||Cylindropuntia acanthocarpa var. colorad|
|3||Branches usually at obtuse angles; stem segments green to dark green, usually short, commonly 8 -20 cm; spines 14-18(-23) per areole, yellow or red-brown, sheaths tight; inner tepals yellow to bronze to brick red||Cylindropuntia acanthocarpa var. major|