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FNA | Family List | FNA Vol. 4 | Cactaceae | Cylindropuntia

20. Cylindropuntia acanthocarpa (Engelmann & J. M. Bigelow) F. M. Knuth in C. Backeberg and F. M. Knuth, Kaktus-ABC. 124. 1935.

Buckhorn cholla

Opuntia acanthocarpa Engelmann & J. M. Bigelow, Proc. Amer. Acad. Arts 3: 308. 1856

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 red-brown, 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.

Varieties 4 (4 in the flora): sw United States, n Mexico.

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....   20b var. thornbe
+ 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 (1) Abaxial 5-7 spines deflexed, usually subparallel, whitish to light brown; tubercles broad, oval; shrubs with few, ascending branches   20a var. acantho
+ 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 (2) 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   20c var. colorad
+ 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   20d var. major


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