Mentzelia oligosperma Sims, rock mentzelia, stick–leaf, chicken thief. Perennial herb, with thick woody roots, typically not rosetted, several—many–stemmed at base, principal branches ascending at midplant with spreading branches forked at each node, in range 20—65 cm tall; shoots typically with only cauline leaves (seedlings with basal leaves), densely pubescent with barbed hairs, hairs pagodalike having barbs in stes (“whorls”), at top most often with a set of downward–pointed (retrorse) barbs (commonly 4—5 at top and grapplelike) but on the plants other hairs with fine–point at tip, lacking glandular hairs.
Stems cylindric, to 5 mm diameter, internodes to 75 mm long, initially densely pubescent mostly with hairs having retrorse barbs at top, aging satiny gray and glabrescent on lower stems where surface layer peels off.
Leaves helically alternate, shallowly pinnately lobed to coarsely serrate, petiolate, without stipules; petiole flat on top, to 5 mm long, indistinct from blade, pale green to tannish, densely pubescent but with fine–pointed hairs on upper side; blade ovate, 18—92 × 12—45 mm, tapered at base, especially large leaves with a pair of lobes at base (sinus < 1/2 to midrib), teeth 2—12 per edge and blade appearing symmetric (paired teeth and lobes) but veined not symmetrically branched to teeth and lobes, acute at tip, pinnately veined with principal veins sunken on upper surface and conspicuously raised on lower surface, upper surface large hairs fine–pointed lacking terminal barbs, lower surface and margin large hairs with terminal retrorse barbs.
Inflorescence leafy cyme, terminal and axillary, several—many–flowered, with a terminal flower later subtended by 0—3 widely diverging branchlets producing a repeatedly forked canopy, bracteate, barbed–hairy like shoot; bractlet subtending pedicel leaflike, to 18 × 12 mm, serrate with < 8 teeth; pedicel cylindric, at anthesis < 1.5 mm long increasing 2× in fruit, densely pubescent with barbed hairs but on upper side larger hairs fine–pointed at tip.
Flower bisexual, radial, 16—22 mm across; calyx deeply 5–lobed, from hypanthium rim, green, densely pubescent on outer (lower) surface and glabrous on inner surface; tube ca. 0.5 mm long; lobes widely spreading, acuminate, 5.8—6.4 × 1—1.2 mm, large hairs along margins fine–pointed at tip, 3–veined from base raised to midpoint on lower surface; petals 5, widely spreading, acuminate–obovate, 8.5—10.5+ × 5—5.5 mm, entire but short–ciliate approaching tip on margins, 5—7–veined at base forking above but not converging at tip, the principal veins raised on lower surface and at base on upper surface, lower surface with fine–pointed hairs above midpoint especially approaching tip; stamens in range 13—19 in 3—4 series, from hypanthium rim, free, all fertile (no staminodes); filaments ascending, unequal, cylindric, 5—7 mm long with the longest in the outer series, yellow–orange, glabrous; anthers dorsifixed, dithecal, 0.7—0.85 mm long, pale yellow, longitudinally dehiscent; pollen whitish to pale yellow; pistil 1, ca. 14 mm long; ovary inferior, ± cylindric, ca. 4 × 1.5 mm (excluding pubescence), green, slightly tapered to base, truncate at tip, densely pubescent with retrorse–barbed hairs, 1–chambered with to 3 ovules attachéd to thick outer wall; nectary disc covering top of ovary to depression with style and slightly extended, ca. 1.3 mm across, pale green, nectar not observed; style ascending, ca. 10 mm long, pale light green, minutely grooved and angled; stigma terminal, minute, colorless, short–papillate.
Fruit capsule, dehiscent by 3 valves at top, 1—3–seeded, cylindric, in range (10—)12—14 × 2.5 mm, pubescent with retrorse barbed hairs; calyx present at top with lobes fused into short ring, abscised at maturity.
Seed ± triangular prismatic, 3.8—4.2 × 1.3—1.6 mm, brown, not winged, the broadest side flat, having a slight ridge on back, surface finely wavy.
A. C. Gibson