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

3. Sclerocactus glaucus (K. Schumann) L. D. Benson, Cact. Succ. J. (Los Angeles). 38: 53. 1966.

Uinta Basin hookless cactus

Echinocactus glaucus K. Schumann, Gesamtbeschr. Kakt., 438. 1898; Ferocactus glaucus (K. Schumann) N. P. Taylor; Pediocactus glaucus (K. Schumann) Arp; Sclerocactus whipplei (Engelmann & J. M. Bigelow) Britton & Rose var. glaucus (K. Schumann) S. L. Welsh

Stems usually unbranched, cylindric to elongate cylindric, 3-12(-28) × 4-9 cm; ribs (8-)12-13(-15), tubercles evident on ribs. Spines slightly or not at all obscuring stems; radial spines (2-)6-8(-12) per areole, white, 0-17 mm; central spines 1-3(-5) per areole, sometimes not greatly different from radial spines; abaxial central spines 0-2 per areole, brown, reddish brown to black, straight (rarely curved or hooked), 12-26 × 0.8-1 mm; lateral central spines 2-4 per areole, similar to abaxial; adaxial central spine 1 per areole, usually white (rarely light brown), elliptic in cross section, 15-31 × 0.5-1.8 mm. Flowers fragrant, funnelform (rarely campanulate), 3-5(-6) × (3-)4-5 cm; outer tepals with greenish lavender midstripes and pink margins, oblanceolate, 25-30 × 4-6 mm; inner tepals pink (rarely pale pink), oblanceolate to lanceolate, 24-30(-35) × 4-6 mm; filaments green to white; anthers yellow. Fruits not regularly dehiscent, ovoid, barrel-shaped, 9-22(-30) × 8-12 mm, dry, with a few membranous scales, mostly near the apex. Seeds black, 1.5 × 2.5 mm; testa with rounded papillae.

Flowering late Apr-May. Exposed, gravel-covered, clay hills, saltbush or sagebrush flats, or pinyon-juniper woodlands; of conservation concern; 1400-2000 m; Colo.

Sclerocactus glaucus is known only from Grand Junction area south to near Montrose, Colorado. The systematic and taxonomic confusion involving S. glaucus has been reviewed by K. D. Heil and J. M. Porter (1994); however, in their revision of Sclerocactus, S. wetlandicus was included within their circumscription of S. glaucus. Chloroplast DNA data (J. M. Porter et al. 2000) are consistent with F. Hochstätter’s (1997) assertion that these represent two taxa. Even so, S. glaucus and S. wetlandicus are morphologically very similar and in the herbarium may be very difficult to discriminate without resorting to scanning electron microscopy (SEM) or a determination based upon geography. The surface of the epidermal cells of S. wetlandicus and S. brevispinus is flattened; this can be observed easily at 20×, but only with some difficulty at 10×. The cells are convex with a flattened apex, like a hill that was strip mined, lacking the conoidal projection; whereas, those of S. glaucus are rounded.


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