Madroño 23: 289, figs. 2C,D. 1976.
Plants candelabra-form, (10–)20–45 cm. Basal leaves persisting or not. Cauline leaves: petiole present or absent (proximal leaves), absent (distal leaves); blade lanceolate to linear (proximal leaves), ovate to linear (distal leaves), to 10(–14) cm, margins dentate or entire (proximal leaves), entire (distal leaves). Bracts green, ovate to elliptic, 4.3–8.3 × 1.9–3.2 mm, width 1/3–2/3 length, not concealing capsule, margins entire. Flowers: sepals 4–10 mm; petals orange proximally, yellow distally, 10–20 mm, apex rounded to retuse; stamens 20+, 4–13 mm, filaments monomorphic, filiform, unlobed; styles 6–14 mm. Capsules narrow-cylindric, 8–35 × 2.5–4 mm, axillary curved to 45° at maturity, often prominently longitudinally ribbed. Seeds 10–20, in 1 row distal to mid fruit, tan, dark-mottled or not, triangular prisms, surface ±smooth to minutely tessellate under 10× magnification; recurved flap over hilum absent; seed coat cell outer periclinal wall flat to slightly convex. 2n = 72.
Phenology: Flowering May–Jul.
Habitat: Yellow to whitish green ash-tuff soils, coarse gravels, steep, open to grassy slopes.
Elevation: 800–1300(–2000) m.
Mentzelia packardiae is the most narrowly distributed species in sect. Trachyphytum, known only from the Leslie Gulch area in eastern Malheur County. During most years, M. packardiae is predominantly limited to barren, ash-derived gravel slopes. A reported collection from Elko County, Nevada, is most likely from a large-flowered population of M. dispersa (N. H. Holmgren et al. 2005). Mentzelia packardiae can be distinguished from M. dispersa by its larger flowers with longer petals [10–20 mm versus 2–6(–8) mm] and styles [6–14 mm versus 2–3.5(–5) mm], and its wider capsules (2.5–4 mm versus 1–2.5 mm).
Mentzelia packardiae is listed as threatened by the Oregon Department of Agriculture and is in the Center for Plant Conservation’s National Collection of Endangered Plants.