Cylindropuntia leptocaulis (DC.) M. F. Knuth, desert christmas cactus, pencil cholla, tasajillo. Shrub, stem succulent, spinescent, cloning and thicket–forming, each individual several–stemmed at base, with photosynthetic green stems, principal branches ascending to spreading, long principal stems commonly bearing many lateral shoots mostly < 60 mm long arising at all or most nodes, clone in range to 120 cm tall; shoot = a series of cylindric stem segments (joints), lateral branches firmly attached and not easily dislodged; major stem woody, principal photosynthetic stems without conspicuous constrictions.
Stems young stems cylindric, 5—7 mm diameter, with helically arranged tubercles (≈ modified leaf bases) and associated areoles (= spine–bearing short shoots) in the axils; tubercles on rapidly growing shoot tip moundlike, to 1 mm high but soon flattening and scarcely raised on mature stem, tubercle having a conspicuous constriction beneath leaf blade, internodes green aging grayish green with thick wax, < 10 mm long, glabrous, cortex and pith watery and mucilaginous; areoles broadly elliptic to roundish, initially 1—2 mm long, covered with tannish hair.
Leaves helically alternate, simple, sessile, without stipules, dimorphic; photosynthetic cauline leaves short–lived on newly emerging shoots, lanceoloid to narrowly ovoid, mostly < 3—6 × 1.3—1.6 mm, fleshy, green, with short point at tip, abscising during shoot expansion; leaf spines on areoles (= modified leaf forms) of two types, persistent spines + deciduous glochids, not photosynthetic; principal, needlelike central spine (0—)1 per areole (subtended by fleshy leaf) + 0—several short lateral spines, unequal, the central spine radiating and nearly ⊥ axis or pressed downward by outgrowth of a new shoot from the areole, slender, to 35 mm long and 0.4 mm diameter at base, round in ×–section, tapered to sharp point, with surface layer separating as a somewhat persistent, scarious, spine sheath (removable with forceps), the sheath yellow or pinkish below midpoint, somewhat inflated so when intact spine appearing wider; deciduous spines (glochids) barbed at tip, irritating in skin, formed in a dense, erect cluster or crescent–shaped group on upper side of areole, mostly 1.3—1.8 mm long, orangish; nectary on areole 0—1, projecting from hair near midpoint of areole, conic, rose–pink, excreting viscid droplet of nectar.
Inflorescence flowers solitary (areole dies after flowering), sessile, with ovary covered by stem tissue hence having tubercles and spine–bearing areoles and short–lived, ovoid cauline leaves; flower initially solitary later with sterile fruits (proliferating) from areoles of fruit producing a second cohort of fruit from the uppermost areoles and often forming vegetative shoots from other areoles after fruit ripens
Flower bisexual, radial, funnel–shaped, ca. 25 mm across; perianth of 15—17 segments; segments helically alternate, overlapping, unequal in a graded size and color series, the outermost 5 segment (without spines in axils) hemi–lanceoloid with membranous margins, 5.5—7 × ± 2.2 mm, green and fleshy, the next series flatter and 8—10 mm long, pale greenish yellow, the inner series of 6—7 segments, 10 mm long with the outermost obovate and ca. 6 mm wide to the innermost segments narrowly ovate and 4.5 mm wide, pale greenish yellow to pale yellow or tinged reddish; perianth abscising from immature fruit as a unit with stamens; stamens many, helically alternate in several series, free, ± monomorphic, formed on a steeply sloped axis 3.5 mm long, at anthesis erect but when touched responding and quickly tilting toward style; filaments ca. 4.5 mm long (outer stamens) to 5.5 mm long (inner stamens), pale greenish yellow or white within depression; anthers dorsifixed, dithecal, 1.2—1.3 mm long, cream–colored, longitudinally dehiscent; pollen cream to pale yellow; pistil 1; ovary inferior, embedded in receptacle (stem tissue), truncate–obovate in outline, at anthesis ca. 13 × 7 mm, with ca. 13 low tubercles, each tubercles bearing an ephemeral ovoid leaf as on stems < 3 mm long; ovary areoles ± round, initially with 1— 3 minutely barbed spines visible (most areoles) and light brown short hair, 1–chambered with ca. 20 ovules attached to wall, chamber oval to broadly obovoid, 2 × 1.5 mm; ovary wall 2 mm thick and mucilaginous; style inversely club–shaped, 10—11 × 1.6—1.8 mm (below stigma), white or greenish white above bulge, surrounded by sunken nectary chamber, nectar scanty; stigmas 4, exserted above central anthers, tonguelike lobes 2 × 1.5 mm, cream–colored, papillate.
Fruit berry, formed with initial fruit and to 4 asexual fruits forming next to upper edge or young vegetative shoots from areoles, mostly lacking seeds but sometimes 20–seeded, subspheroid or broadly ellipsoid to obovoid, in range 13—21 × (7—)9—12.5 mm, red and fleshy, with glochids or sometimes with to 7 short spines to 4 mm long on an areole, top depressed ca. 2 mm
Seed compressed and roundish to angular in outline, in range 3.8—4.7 mm, ca. 1 mm thick, dull pale yellow, with slight dimple or depression on each face, with narrow girdle along edge, often inconspicuously notched at hilum.
A. C. Gibson