Plants few branched or un-branched. Stems depressed-ovoid or occasionally elongate-cylindric, 5-15(-25) × 6-11.5 cm; areoles circular to pyriform, villous to lanate. Spines distin-guishable as radial and central: radial spines 11-15 per areole, white, 11-21 mm; central spines 3-7 per areole, nearly porrect, brownish black aging to pale gray or white, straight or slightly curving at tips, 13-30 × 1 mm at base. Flowers 0.8-2.2 × 2-3 cm; scales long fringed; outer tepals brown with white margins, long fringed, 9-15 × 3-4.5 mm; inner tepals yellow with purple veins, 15-20 × 4.5-6 mm. Fruits greenish yellow, short cylindric, 12-15 × 6-9 mm. Seeds gray to nearly black, 3.5-5 × 3-3.5 mm, papillate and rugose.

Flowering spring. Rounded hills in gypsum clay and sandy soils of Moenkopi Formation, Great Basin desert scrub; of conservation concern; 900-1600 m; Ariz., Utah.

Pediocactus sileri stems tend to develop a basal thatch of spines that anchor it to the fine, gypsum-rich soil. This species is endemic to a narrow strip along the Arizona-Utah border.

Plant: STEMS usually solitary or a few in clusters, depressed-ovoid, ovoid, or occasionally elongate-cylindrical, 5-15(-25) cm long, 6-11.5 cm in diameter, apex of the stem 3-11(-20) cm above soil surface; tubercles truncate-conical, 9-12 mm long, 6-11 mm in diameter, older tubercles dry, corky, compressed and persistent; areoles circular, woolly

Leaves: SPINES densely covering the stem, the older spine clusters frayed, weathered, persistent and forming a thatch at the base of the stem; central spines 3-5(-7), 1.3-3 cm long, mostly 1 mm wide at the base, brownish-black aging to pale gray or white, nearly porrect, straight or slightly curving at the tips, acicular, nearly circular in cross section; radial spines 11-15, 1.1-2.1 cm long, white

Flowers: up to 2.2 cm long, about 2.5 cm wide; outer tepals brown with white fringes; inner tepals yellow, obovate-oblanceolate, 1.5-1.9 cm long; 4.5-6 mm broad, minutely denticulate; stigma lobes yellow

Fruit: FRUITS greenish-yellow, 1.2-1.5 cm long, 6-9 mm in diameter, scales present, cylindrical, dehiscing by a vertical slit. SEEDS gray to black, finely papillate and rugose, obliquely pyriform, 3.5-5 mm long, 3-3.5 mm wide

Misc: Desertscrub; 1500 m (5000 ft.); May

REFERENCES: Heil, Kenneth D., and Mark J. Porter. 2001. Cactaceae. J. Ariz. - Nev. Acad. Sci. Volume 33(1)