Sclerocactus

Plants erect, usually unbranched, sometimes deep-seated in substrate in winter but never flat-topped. Roots diffuse. Stems unsegmented, pale to dark green or bluish green, ovoid, spheric, depressed-spheric, depressed hemispheric, cylindric, or elongate cylindric, 1–40(–45) × 1.8–15(–20) cm, occasionally glaucous; tubercles usually coalescent into ribs (rarely remaining as separate tubercles); ribs 10–17(–20), crests deeply notched above each areole, thus ribs tuberculate; tubercles ± prominent on ribs; areoles 8–20 mm apart, elliptic to pyriform, with fertile portion as short adaxial prolongation confluent with spine cluster or connected to spine cluster by very broad groove, woolly; areolar glands few or absent; cortex and pith highly mucilaginous. Spines 2–17(–29); radial spines 2–11(–18) per areole, usually white or gray, sometimes straw colored, brown, pink, purplish pink, or black, straight or curved; central spines (0–)1–6(–11) per areole, gray, white, yellow, straw colored, red, reddish brown, brown, pink to purplish pink or black, usually of 2–3 distinct types, 1 or more hooked (rarely none hooked), acicular or subulate, or both (ribbonlike and papery in S. papyracanthus), longest spines 7–15 mm. Flowers diurnal, borne at adaxial edge of areoles at or near stem apex or in short extension of spine-bearing areoles, campanulate or funnelform, 1–6.7 × 1–6(–7) cm; outer tepals with greenish lavender, reddish brown, yellowish brown, or purple midstripes, white, cream, gold, rose, pink, or purple margins, oblanceolate, 10–45 × 3–10 mm, margins entire or fimbriate; inner tepals erect to ascending white, cream, yellow, or pink to purplish, often with dark midstripes, lanceolate to oblanceolate, 15–50 × 4–12 mm, margins entire or fimbriate; ovary scaly, spineless; stigma lobes 5–12, pink, green, yellow, or creamy white, 1.5–3.5 mm. Fruits dehiscent along 2–4 irregular, short vertical slits above base, or through basal abscission pore, green, often turning tan, pink or red, cylindric to subspheric, 4.2–30 × 3.5–21(–25) mm, thin walled, fleshy, becoming dry at maturity, naked or with few broad, thin scales; pulp greenish to white, scant; floral remnant persistent. Seeds brown or black, 1.5–3 × 1.9–4.5 mm, glossy or shiny; testa papillate (rarely furrowed). x = 11.

Distribution

w United States.

Discussion

Species 15 (15 in the flora).

There has been considerable controversy concerning generic circumscription of Sclerocactus. Some treatments include Ancistrocactus, Echinomastus, Glandulicactus, and Sclerocactus as a single genus; whereas others exclude those groups, in addition to Toumeya, from Sclerocactus. Molecular phylogenetic studies of chloroplast DNA sequences (J. M. Porter et al. 2000; R. Nyffeler 2002) support a close relationship among Ancistrocactus, Echinomastus, Toumeya, and Sclerocactus; only Toumeya is included with Sclerocactus here. Although morphologically cohesive, Echinomastus is inferred to be a paraphyletic group, with some species (i.e., E. johnsonii) more closely related to Sclerocactus than to other members of Echinomastus. Ancistrocactus is sister to Echinomastus and Sclerocactus, providing merit to a broader circumscription of Sclerocactus. Glandulicactus and Pediocactus are only distantly related to this group, bolstering their exclusion from Sclerocactus.

Toumeya Britton & Rose is an illegitimate name that pertains here.

Selected References

Heil, K. D. and J. M. Porter. 1994. Sclerocactus (Cactaceae): A revision. Haseltonia 2: 20–46.

Hochstätter, F. 1995. The genus Sclerocactus (Cactaceae)—Part 1. Cact. Succ. J. Gr. Brit. 13: 73–79.

Hochstätter, F. 1996. The genus Sclerocactus (Cactaceae)—Part 2. Cact. Succ. J. Gr. Brit. 14: 76–84.

Hochstätter, F. 1996b. The genus Sclerocactus (Cactaceae)—Part 3. Cact. Succ. J. Gr. Brit. 14: 183–188.

Hochstätter, F. 1997. The genus Sclerocactus (Cactaceae)—Part 4. Cact. Succ. J. Gr. Brit. 15: 74–81.

Lower Taxa

Sclerocactus blainei, Sclerocactus brevispinus, Sclerocactus cloverae, Sclerocactus glaucus, Sclerocactus mesae-verdae, Sclerocactus nyensis, Sclerocactus papyracanthus, Sclerocactus parviflorus, Sclerocactus polyancistrus, Sclerocactus pubispinus, Sclerocactus sileri, Sclerocactus spinosior, Sclerocactus wetlandicus, Sclerocactus whipplei, Sclerocactus wrightiae

Key

1	Central spines (0-)1(-4) per areole, ribbonlike, flexible, twisting or curled, papery, with obscure adaxial midrib, lacking hook, if central spine absent, then radial spines strongly flattened	Sclerocactus papyracanthus
1	Central spines (0-)1-6(-11) per areole, terete to angled, or if all flattened and papery, then some hooked, if central spine absent, then radial spines not flattened	> 2
2	Abaxial central spine nearly always absent, if present, then hooked, 7-15 mm, brown; flowers yellow or cream (rarely pink); nw New Mexico and sw Colorado	Sclerocactus mesae-verdae
2	Abaxial central spines nearly always present, usually hooked (sometimes straight), 10-100 mm, variable in color; flowers variable in color, but if from nw New Mexico, then deep pink to purple, never cream to golden; widespread	> 3
3	Fruits dehiscent by 1-4 vertical slits forming before fruits dry	> 4
3	Fruits not vertically dehiscent, irregularly shattering when dry or dehiscent through basal abscission pore and easily removed when fruits still succulent	> 7
4	Flowers yellowish, 2.5-3 cm; inner tepal margins crisped or minutely toothed; styles minutely but densely papillate; radial spines usually 6-8 per areole, to 15 mm; nc Arizona	Sclerocactus sileri
4	Flowers lavender, red-purple, pink, or yellow, 2-5 cm; inner tepal margins entire to minutely toothed; styles very minutely and sparsely papillate, appearing smooth; radial spines usually 8-11 per areole, to 35 mm; w Utah, Nevada	> 5
5	Flowers cream with yellow, greenish, reddish purple, lavender, or brownish margins; inner tepal apices generally rounded, usually not mucronate; adaxial central spine usually to 25 mm, 0.7 mm wide at base	Sclerocactus pubispinus
5	Flowers usually violet to rose or pink (rarely cream); inner tepal apices usually mucronate; adaxial central spine to 30-50+ mm, to 16 mm wide at base	> 6
6	Central spines pubescent only in very young, pre-reproductive plants; lateral central spines 10-30 mm, terete; adaxial central spines 1-3 per areole, 0.7-1.6 mm diam	Sclerocactus spinosior
6	Central spines pubescent in young and early reproductive plants; lateral central spines 10-40 mm, usually terete, sometimes flattened and ribbonlike; adaxial central spine usually 1 per areole, 1.5-2.5 mm diam	Sclerocactus blainei
7	Hooked spines typically 5 or more per areole; California, Nevada	> 8
7	Hooked spines 0-4 per areole; Arizona, Colorado, New Mexico, Utah	> 9
8	Central spines usually 9-12 per areole; radial spines 20-50 mm; flowers 5-10 cm; fruits 2.2-5 cm; California, Nevada	Sclerocactus polyancistrus
8	Central spines usually 6-8 per areole; radial spines 8-20 mm; flowers 3-4 cm; fruits 1.5-2 cm; Nevada	Sclerocactus nyensis
9	Central spines straight, not hooked, if hooked, then shorter than 10 mm	> 10
9	Abaxial central spine hooked, generally longer than 10 mm	> 12
10	Seed surface composed of convex cells; Colorado	Sclerocactus glaucus
10	Seed surface composed of flattened cells; Utah	> 11
11	Abaxial central spines usually not hooked; perianth funnelform; outer and inner tepals brownish lavender, violet, or pink, 2.5-5 cm diam	Sclerocactus wetlandicus
11	Abaxial central spines often absent, or if present, then all curved or hooked; perianth campanulate; outer tepals greenish to purple, inner tepals purple, 1.1-3 cm diam	Sclerocactus brevispinus
12	Flowers 2.2-3.5 × 1.5-3.5 cm; ovary minutely papillate, appearing smooth; adaxial central spine 1.5-2 mm wide, or if less than 1.5 mm wide, then radial spines 4-6 per areole; radial spines 4-12 per areole	> 13
12	Flowers 3-5.7 × 2-5.5 cm; ovary papillate, appearing granular; adaxial central spine 0.5-1.5 mm wide; radial spines 5-17 per areole	> 14
13	Flowers yellow; radial spines 7-12; ne Arizona, se Utah	Sclerocactus whipplei
13	Flowers purple; radial spines 4-6; sw Colorado, nw New Mexico	Sclerocactus cloverae
14	Flowers pale pink to white or cream; filaments magenta; central spines (3-)4 per areole, abaxial spine white to tan, 10-30 mm; fruits 0.9-1.5 cm	Sclerocactus wrightiae
14	Flowers purple, pink, or yellow (rarely white); filaments green to whitish, or if magenta, then flowers not pale pink or white; central spines 4-8 per areole, abaxial spine usually purple-black, 15-72 mm; fruits 1-3 cm	Sclerocactus parviflorus