Desert Christmas cholla, Christmas cactus

Opuntia leptocaulis de Candolle, Mém. Mus. Hist. Nat. 17: 118. 1828; Cylindropuntia leptocaulis var. brevispina (Engelmann) F. M. Knuth; C. leptocaulis var. longispina (Engelmann) F. M. Knuth; O. fragilis Nuttall var. frutescens Engelmann; O. frutescens (Engelmann) Engelmann; O. frutescens var. brevispina Engelmann; O. frutescens var. longispina Engelmann; O. leptocaulis var. brevispina (Engelmann) S. Watson; O. leptocaulis var. longispina (Engelmann) A. Berger; O. leptocaulis var. vaginata (Engelmann) S. Watson; O. vaginata Engelmann

Shrubs or small trees, sparingly to densely branched, 0.5-1.8 m, usually bearing similar, commonly spineless terminal branchlets arranged at right angles along major axes. Stem segments usually alternate, gray-green or purplish, 2-8 × 0.3-0.5 cm; tubercles linear, drying as elongate, riblike wrinkles, 1.1-2(-3) cm; areoles broadly elliptic, (1-)1.5-3.5 × 0.7-2 mm; wool white to yellow, aging gray. Spines 0-1(-3) per areole, usually in apical areoles to well distributed, erect, flexible, straight or arching upward or downward, red-brown with gray to whitish coat, tips yellow, aging red-brown, terete, angular-flattened basally, the longest (4-)14-45 mm; sheaths gray to purple-gray with yellow to red-brown tips or yellow throughout. Glochids in adaxial tuft or crescent to encircling areole, yellow or reddish brown, 1-3(-5) mm. Flowers: inner tepals pale yellow to greenish yellow, sometimes tipped red, narrowly obovate, 5-8 mm, acute, apiculate; filaments greenish yellow; anthers yellow; style yellow; stigma lobes greenish yellow. Fruits occasionally proliferating, yellow to scarlet (rarely green, sometimes tinged purple, becoming yellow), sometimes stipitate, obovoid, 9-15(-27) × 6-7(-12) mm, fleshy, smooth, spineless; umbilicus 2-4 mm deep; areoles 16-20. Seeds pale yellow, suborbicular to squarish and crenate in outline, warped, 3-4.5 mm diam., sides smooth, each with 1-3 large depressions; girdle smooth or with very narrow ridge. 2n = 22, 33, 44.

Flowering spring-early summer, sometimes fall (Mar-Aug, Oct). Deserts, grasslands, chaparrals, oak-juniper woodlands, flats, bajadas and slopes, sandy, loamy to gravelly substrates; 40-1500 m; Ariz., N.Mex., Okla., Tex.; Mexico (Chihuahua, Coahuila, Durango, Nuevo León, Sonora, Tamaulipas, Zacatecas).

Cylindropuntia leptocaulis forms hybrids with C. acanthocarpa var. major (see 3. C. ×tetracantha), C. arbuscula, C. fulgida, C. kleiniae, C. spinosior, C. versicolor (see discussion under C. ×tetracantha), and C. whipplei. Hybrids in central Arizona have flowers intermediate in size to the parents, narrow tuberculate stems bearing 0-1(-2) major spines per areole, and tuberculate, spineless, orange to red fruits. The chromosome number reported for hybrids is 2n = 22.