Novon 19: 119. 2009.
Plants perennial, bushlike, with subterranean caudices or rhizomes. Stems multiple, erect, zigzag; branches distal or along entire stem, distal longest or all ± equal, antrorse, straight to upcurved; hairy. Leaves: blade 14–26.3 × 5.1–10.8 mm, widest intersinus distance 2.3–5.2 mm; proximal oblanceolate to elliptic, margins usually 3-fid, rarely entire or pinnate, teeth or lobes usually 2, rarely 0 or 4, perpendicular to leaf axis, 0.8–2.7 mm; distal elliptic, base not clasping, margins 3-fid to occasionally pinnate, teeth or lobes usually 2, occasionally 4, perpendicular to leaf axis, 1.5–3.5 mm; abaxial surface with simple grappling-hook and complex grappling-hook trichomes, adaxial surface with simple grappling-hook and needlelike trichomes. Bracts: margins usually entire, rarely pinnate. Flowers: petals golden yellow, 8.3–13.6 × 2.6–4.8(–6.2) mm, apex acute, glabrous abaxially; stamens golden yellow, 5 outermost petaloid, filaments broadly spatulate, strongly clawed, 6–8(–9.1) × 2.3–4.4 mm, with anthers, second whorl with anthers; anthers straight after dehiscence, epidermis smooth; styles 5–7.9 mm. Capsules cup-shaped, 4–7.3 × 3.3–5.8 mm, base rounded, not longitudinally ridged. Seeds: coat anticlinal cell walls straight, papillae 4–5 per cell.
Phenology: Flowering Jun–Sep.
Habitat: Barren gray soils, steep shale slopes.
Elevation: 1700–2100 m.
Mentzelia librina in narrowly distributed along the border between Carbon and Emery counties.