Mentzelia obscura |
Mentzelia holmgreniorum |
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Pacific blazing star |
Holmgrens' blazingstar |
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Habit | Plants candelabra-form, 8–45 cm. | Plants biennial, candelabra-form. |
Stems | solitary, erect, straight; branches distal or along entire stem, distal or proximal longest, antrorse, upcurved; hairy. |
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Leaves | blade 42–89 × 11–31.9 mm, widest intersinus distance 2.3–3.6 mm; proximal oblanceolate to elliptic, margins pinnatisect, lobes 14–20, strongly antrorse, 4.9–14.4 mm; distal lanceolate, base not clasping, margins pinnatisect, lobes 12–18, strongly antrorse, 4.2–12.4 mm; abaxial surface with simple grappling-hook, complex grappling-hook, and needlelike trichomes, adaxial surface with simple grappling-hook and needlelike trichomes. |
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Basal leaves | persisting; petiole present or absent; blade linear-lanceolate to linear, margins usually irregularly deeply lobed, lobes pointed. |
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Cauline leaves | petiole absent; blade ovate-lanceolate to linear, to 15(–22) cm, margins few-lobed or entire. |
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Bracts | green, ovate to ovate-lanceolate, 2.9–8.2 × 1.1–1.9 mm, width 1/8–1/2 length, not concealing capsule, margins entire. |
margins pinnate. |
Flowers | sepals 2–6 mm; petals yellow to orange proximally, yellow distally, 3–8 mm, apex rounded or acute apex; stamens 20–40, 2–7 mm, filaments monomorphic, filiform, unlobed; styles 2–6 mm. |
petals golden yellow, 13.5–18.8 × 5.2–6.6 mm, apex rounded, glabrous abaxially; stamens golden yellow, 5 outermost petaloid, filaments narrowly spatulate, slightly clawed, 11.1–16 × 2.7–5 mm, without anthers, second whorl with anthers; anthers straight after dehiscence, epidermis smooth; styles 8.4–10.6 mm. |
Capsules | clavate, 11–31 × 1.5–3 mm, axillary curved to 250° at maturity, usually inconspicuously longitudinally ribbed. |
cylindric, 13.1–14.6 × 5.8–6.9 mm, base tapering, not longitudinally ridged. |
Seeds | 15–50, 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 colliculate under 10x magnification; recurved flap over hilum absent; seed coat cell outer periclinal wall domed, domes on seed edges less than 1/2 as tall as wide at maturity. |
coat anticlinal cell walls sinuous, papillae 26–51 per cell. |
2n | = 36. |
= 20. |
Mentzelia obscura |
Mentzelia holmgreniorum |
|
Phenology | Flowering Feb–May. | Flowering Jun–Aug. |
Habitat | Sandy to rocky washes or slopes, desert scrub, Joshua-tree woodlands, roadsides. | Dry sandy washes, roadsides, disturbed areas. |
Elevation | 200–1700 m. (700–5600 ft.) | 1400–2300 m. (4600–7500 ft.) |
Distribution |
AZ; CA; NV; UT; Mexico (Baja California, Sonora)
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AZ; NM |
Discussion | Mentzelia obscura is morphologically intermediate to M. desertorum and M. albicaulis and is known to occur in mixed populations with both species. Reliable discrimination among these species usually requires mature seeds. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Mentzelia holmgreniorum is known from Apache, Coconino, and Navajo counties, Arizona, and Catron County, New Mexico. It is allopatric from the species most similar to it (M. filifolia, M. laciniata, and M. lagarosa), occurring south and west of all three; it differs from all these species in having upcurved rather than straight branches, and from M. filifolia and M. laciniata in having both simple grappling-hook and needlelike trichomes (versus only needlelike trichomes) on its adaxial leaf surfaces. In addition, M. holmgreniorum differs from M. filifolia in having leaf blades with greater intersinus distances (2.3–3.6 mm versus 1–2.4 mm) and wider lobes (1.6–2.5 mm versus 0.8–1.4 mm), from M. laciniata in having pinnate bracts (versus usually entire, rarely pinnate), and from M. lagarosa in having leaf blade lobes that are strongly antrorsely oriented (versus slightly antrorsely or perpendicular to the leaf axis) and flowers with larger petals (13.5–18.8 × 5.2–6.6 mm versus 8.3–13 × 2.2–5.4 mm) and longer outermost stamens (11.1–16 mm versus 6.5–10.7 mm). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 540. | FNA vol. 12, p. 516. |
Parent taxa | Loasaceae > Mentzelia > sect. Trachyphytum | Loasaceae > Mentzelia > sect. Bartonia |
Sibling taxa | ||
Name authority | H. J. Thompson & J. E. Roberts: Phytologia 21: 284. (1971) | J. J. Schenk & L. Hufford: Madroño 57: 252, fig. 2C. (2010) |
Web links |