69. Mentzelia desertorum (Davidson) H. J. Thompson & J. E. Roberts, Phytologia. 21: 280. 1971.
Desert blazingstar Desert blazingstar
Acrolasia desertorum Davidson, Bull. S. Calif. Acad. Sci. 5: 16. 1906
Plants candelabra-form, 5–40 cm. Basal leaves persisting; petiole present or absent; blade linear, margins usually shallowly lobed, lobes rounded. Cauline leaves: petiole absent; blade ovate-lanceolate to linear, to 12 cm, margins shallowly lobed or entire. Bracts green, ovate to ovate-lanceolate, 3.6–4.7 × 1.6–2.3 mm, width 1/3–1/2 length, not concealing capsule, margins entire. Flowers: sepals 2–4 mm; petals yellow to orange proximally, yellow distally, 2–6 mm, apex acute or rounded; stamens 10–30, 2–4 mm, filaments monomorphic, filiform, unlobed; styles 2–4 mm. Capsules clavate, 12–27 × 1–2.5 mm, axillary curved to 180° at maturity, usually inconspicuously longitudinally ribbed. Seeds 10–50, in 2+ rows distal to mid fruit, tan, usually not, occasionally sparsely, dark-mottled, usually irregularly polygonal, occasionally triangular prisms proximal to mid fruit, surface tessellate under 10× magnification; recurved flap over hilum absent; seed coat cell outer periclinal wall flat to slightly convex. 2n = 18.
Flowering Feb–Mar. Sandy flats, washes, creosote-bush scrub; of conservation concern; 30–1000 m; Ariz., Calif.; Mexico (Baja California, Sonora).
Mentzelia desertorum, a diploid, is most similar morphologically to the tetraploid M. obscura, and the two species may be difficult to distinguish prior to seed maturation. However, many populations of M. desertorum have narrow basal leaves with short, widely spaced lobes that are unique among species within sect. Trachyphytum.