15. Sclerocactus papyracanthus (Engelmann) N. P. Taylor, Bradleya. 5: 94. 1987.
Grama-grass cactus, paper-spined cactus, toumeya
Mammillaria papyracantha Engelmann, Mem. Amer. Acad. Arts, n. s. 4: 49. 1849; Pediocactus papyracanthus (Engelmann) L. D. Benson; Toumeya papyracantha (Engelmann) Britton & Rose
Stems unbranched, cylindric or obconic cylindric, 2-7.5(-8) × 1.2-2.5 cm; ribs not evident, tubercles prominent. Spines dense, obscuring stems; radial spines 5-10 per areole, white, straight, flat, (2-)3-5 × 0.3-0.6 mm; central spines 1(-4) per areole; abaxial central spine 1 per areole, whitish to tan or gray, straight, wavy, twisting, or curling, flat, flexible, papery, with obscure adaxial midrib, sometimes pointing upward and obscuring apex of plant, lacking hook, 15-45(-50) × 1-1.5 mm; lateral or adaxial central spines 0(-3) per areole, white to tan, (3-)20-40 × 0.5-1 mm. Flowers funnelform to narrowly campanulate, 2-2.5 × 1-2.5 cm; outer tepals with green-purple to red-brown midstripes and cream to white margins, cuneate-spatulate, usually 9-20 × 1-3 mm, finely toothed; inner tepals white with brown midstripes, largest tepals oblanceolate, 15-20 × 3.5-4.5 mm, apex acute to mucronate; filaments white to greenish yellow; anthers cream to pale yellow. Fruits indehiscent or irregularly dehiscent, green, subspheric, 4-6 × 3-5 mm, dry at maturity; scales few or none. Seeds black, 2.5-3 × 2-2.5 mm, shiny; testa with fine, rounded papillae.
Flowering Apr-Jun. Desert grasslands, pinyon-juniper woodlands, Chihuahuan desert scrub; 1500-2200 m; Ariz., N.Mex., Tex.
With long, flexuous, flattened spines and pale flowers, Sclerocactus papyracanthus is surprisingly cryptic in the field. There has been a long debate concerning its taxonomic placement. Chloroplast DNA analyses of J. M. Porter et al. (2000) unambiguously placed this species within Sclerocactus, a position first suggested based on morphologic evidence (K. D. Heil et al. 1981; C. Glass and R. A. Foster 1984).