Mentzelia obscura |
Mentzelia involucrata |
|
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Pacific blazing star |
sand blazing star, white-bract blazing star |
|
Habit | Plants candelabra-form, 8–45 cm. | Plants 7–35(–45) cm. |
Basal leaves | persisting; petiole present or absent; blade linear-lanceolate to linear, margins usually irregularly deeply lobed, lobes pointed. |
petioles present or absent; blade lanceolate, to 10(–16) cm; margins shallowly to deeply lobed, lobes acute. |
Cauline leaves | petiole absent; blade ovate-lanceolate to linear, to 15(–22) cm, margins few-lobed or entire. |
petioles absent; blade ovate to lanceolate, to 10(–16) cm, base often cordate-clasping, margins deeply to shallowly lobed, lobes acute. |
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. |
white with green margins, conspicuous, concealing pedicel, ovary, and capsule. |
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 white to pale yellow, usually with orange veins, obovate, 13–65 mm, apex mucronate; stamens 4–26 mm, less than 1/2 petal length, all fertile, none petaloid (flowers appearing to have 5 petals); filaments ± monomorphic, linear, distally 2-lobed, lobes 0.5–2 mm; anther stalk shorter or longer than filament lobes; style 8–30 mm. |
Capsules | clavate, 11–31 × 1.5–3 mm, axillary curved to 250° at maturity, usually inconspicuously longitudinally ribbed. |
cylindric to cup-shaped, 14–25(–30) × 5–10 mm, erect. |
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. |
usually constricted proximal to middle; seed coat anticlinal cell walls wavy. |
2n | = 36. |
= 18. |
Mentzelia obscura |
Mentzelia involucrata |
|
Phenology | Flowering Feb–May. | Flowering Jan–May. |
Habitat | Sandy to rocky washes or slopes, desert scrub, Joshua-tree woodlands, roadsides. | Washes, fans, slopes, desert scrub. |
Elevation | 200–1700 m. (700–5600 ft.) | 50–900 m. (200–3000 ft.) |
Distribution |
AZ; CA; NV; UT; Mexico (Baja California, Sonora)
|
AZ; CA; Mexico (Baja California, Sonora)
|
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 involucrata is easily distinguished from other species in sect. Bicuspidaria by its large white bracts, which are strikingly similar to those of M. congesta in sect. Trachyphytum. Phylogenetic studies show that these species are not closely related, suggesting a homoplasious origin of the characteristic (J. M. Brokaw and L. Hufford, 2010). Populations exhibiting petals longer than 3 cm have previously been called var. megalantha. However, a study by G. S. Daniels (1970) suggested that insufficient geographic and morphological discontinuities exist for recognition of varieties. P. A. Munz (1974) mistakenly cited var. megalantha as Mentzelia involucrata subsp. megalantha I. M. Johnston, a name never validly published. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 540. | FNA vol. 12, p. 525. |
Parent taxa | Loasaceae > Mentzelia > sect. Trachyphytum | Loasaceae > Mentzelia > sect. Bicuspidaria |
Sibling taxa | ||
Synonyms | M. involucrata var. megalantha | |
Name authority | H. J. Thompson & J. E. Roberts: Phytologia 21: 284. (1971) | S. Watson: Proc. Amer. Acad. Arts 20: 367. (1885) |
Web links |