Mentzelia sect. Trachyphytum
Mentzelia albicaulis
small flower blazing star, small-flower evening star, white stem blazing star, white-stem evening star, white-stem stick-leaf
basal rosette present, persistent or not, proximalmost internodes to 5 mm;
blade without broad basal lobes, margins entire, toothed, pinnate, or pinnatisect, flat.
persisting;
petiole present or absent;
blade linear-lanceolate to linear, margins deeply to shallowly lobed.
petiole absent;
blade ovate-lanceolate to linear, to 15 cm, margins deeply to shallowly lobed or entire.
green, ovate to linear, 3.7–8.6 × 0.8–3.9 mm, width 1/6–2/3 length, not concealing capsule, margins 3-lobed or entire, lateral lobes never prominent.
stamens all fertile, filaments monomorphic, filiform, or heteromorphic, 5 outermost dorsiventrally flattened, linear or elliptic, not petaloid, inner filiform, usually unlobed, rarely distally 2-lobed;
ovules (and seeds) oriented parallel to long axis of ovary.
sepals 1–5 mm;
petals orange proximally, yellow distally, 3–7(–8) mm, apex usually acute, rarely retuse;
stamens 20+, 3–5 mm, filaments monomorphic, filiform, unlobed;
styles 2–5 mm.
cylindric or clavate, axillary straight to strongly curved, sometimes S-shaped, terminal straight to slightly curved.
clavate, 8–28(–35) × 1.5–3.5 mm, longest capsules usually 15+ mm, axillary curved to 180° at maturity, usually inconspicuously longitudinally ribbed.
triangular prisms with grooves along longitudinal edges or irregularly polygonal (angular or rounded), not winged (occasionally winged in M. lindleyi);
seed coat cells polygonal, ± isodiametric, anticlinal walls straight.
10–30, in 2+ rows distal to mid fruit, dark brown or tan, moderately to densely dark-mottled, usually irregularly polygonal, occasionally triangular prisms proximal to mid fruit, surface tuberculate under 10x magnification; recurved flap over hilum absent;
seed coat cell outer periclinal wall domed, domes on seed edges more than 1/2 as tall as wide at maturity.
= 54, 72.
Mentzelia sect. Trachyphytum
Mentzelia albicaulis
Species ca. 22 (21 in the flora).
Both homoploid hybridization and allopolyploidy have played important roles in the diversification of sect. Trachyphytum (J. M. Brokaw 2009; Brokaw and L. Hufford 2010, 2010b). H. J. Thompson and H. Lewis (1953) and J. E. Zavortink (1966) reported diploid, tetraploid, hexaploid, and octoploid species in the section. The small desert and grassland annuals of this section are often difficult to distinguish due to the simplicity of their shoot systems, inter-population variability, and morphological intermediacy of allopolyploids. In contrast, homoploid hybridization appears to be rare among existing populations. Evidence of homoploid hybridization has been found primarily in molecular studies (Brokaw and Hufford 2010) and has been observed in natural populations only among hexaploid species (Zavortink).
Seed characteristics have been some of the most reliable characters for discrimination of the common, widespread species but often require an advanced developmental stage for observation. However, the two major clades in sect. Trachyphytum, “Affines” [containing Mentzelia affinis, M. dispersa, and M. micrantha (J. M. Brokaw and L. Hufford 2010)] and “Trachyphyta” [containing all other diploids and most polyploids (Brokaw and Hufford 2010, 2010b)], can be distinguished relatively early in seed development. Even when immature, plants of the “Affines” clade have a single triangular ovule in the cross-sectional view of the top of the ovary. With the exception of the narrowly distributed M. packardiae, immature plants of the “Trachyphyta” clade have two or more ovules at the top of the ovary. Further, these two groups differ in the size of their seed coat cells, which can be distinguished early in seed development: cells of the “Affines” clade are small and barely discernible at 10× magnification, whereas those of the “Trachyphyta” clade are large and clearly visible at 10× magnification, resulting in a tessellate to tuberculate appearance of the seed coat.
The only species in sect. Trachyphytum not found in the flora area is the South American Mentzelia bartonioides (C. Presl) Urban & Gilg.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Mentzelia albicaulis is the most widespread species in sect. Trachyphytum and exhibits extensive morphological variation. Most populations of M. albicaulis are octoploid; however, hexaploids from southern California that have been called M. mojavensis and occasionally M. californica are also treated here as M. albicaulis. Two tetraploids in sect. Trachyphytum, M. montana and M. obscura, also have been treated previously as M. albicaulis (N. H. Holmgren et al. 2005). Both exhibit morphological forms and distributions overlapping with M. albicaulis. However, in most cases these species can be distinguished without chromosome counts, and their distinctiveness has been supported by phylogenetic analyses (J. M. Brokaw and L. Hufford 2010b).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Seeds in 1 row distal to mid fruit, triangular prisms. | → 2 |
2. Stamen filaments heteromorphic, 5 outermost elliptic, distally 2-lobed, inner filiform, unlobed. | M. micrantha |
2. Stamen filaments monomorphic, filiform, unlobed. | → 3 |
3. Petals 10–20 mm; styles 6–14 mm; Malheur County, Oregon. | M. packardiae |
3. Petals 2–12 mm; styles 2–6.5 mm; w North America, including Malheur County, Oregon. | → 4 |
4. Blades of basal leaves usually deeply to moderately lobed, sinuses extending more than 1/4 to midvein, rarely entire; styles 3–6.5 mm; capsules often prominently longitudinally ribbed; Arizona, s California, below 1200 m. | M. affinis |
4. Blades of basal leaves usually dentate, sinuses extending less than 1/4 to midvein, or entire, rarely deeply lobed; styles 2–3.5(–5); capsules usually inconspicuously longitudinally ribbed; w North America, including Arizona and s California, where above 1200 m. | M. dispersa |
1. Seeds in 2+ rows distal to mid fruit, irregularly polygonal or occasionally triangular prisms proximal to mid fruit. | → 5 |
5. Basal leaves not persisting; blade margins of proximalmost remaining leaves (proximal cauline) dentate or entire; usually on barren, alkaline or saline soils. | → 6 |
6. Petals 8–12 mm; sepals 3–5.5 mm; Idaho, Nevada, Oregon. | M. mollis |
6. Petals 2–4 mm; sepals 1–3 mm; Colorado, New Mexico, Utah. | M. thompsonii |
5. Basal leaves persisting; blade margins of proximalmost leaves (basal) usually deeply to shallowly lobed, rarely entire; on wide variety of substrates. | → 7 |
7. Bract margins entire, bracts green. | → 8 |
8. Petals (6–)8–25 mm. | → 9 |
9. Sepals (7–)9–16 mm; styles 7–15 mm; e Kern County and nw San Bernardino County, California. | M. eremophila |
9. Sepals (2–)3–8(–10) mm; styles 4–10 mm; Arizona, e California, Nevada. | → 10 |
10. Seeds without recurved flap over hilum; seed coat cell outer periclinal wall domes on seed edges more than 1/2 as tall as wide at maturity. | M. jonesii |
10. Seeds usually with recurved flap over hilum; seed coat cell outer periclinal wall domes on seed edges less than 1/2 as tall as wide at maturity. | M. nitens |
8. Petals 2–8 mm. | → 11 |
11. Seeds dark brown or tan and moderately to densely dark-mottled; seed coat cell outer periclinal walls domed, domes on seed edges more than 1/2 as tall as wide at maturity. | M. albicaulis |
11. Seeds tan, not or occasionally sparsely dark-mottled; seed coat cell outer periclinal walls flat to slightly convex, or if domed, domes on seed edges less than 1/2 as tall as wide. | → 12 |
12. Capsules 6–15 mm, axillary curved to 20°; 2000–2500 m; Mono County, California. | M. monoensis |
12. Capsules 11–31 mm, axillary curved to 250°; 30–1700 m; sw United States, but not Mono County, California. | → 13 |
13. Blade margins of basal leaves usually shallowly lobed, lobes rounded; seed coat cell outer periclinal walls flat or slightly convex. | M. desertorum |
13. Blade margins of basal leaves usually deeply lobed, lobes pointed; seed coat cell outer periclinal walls domed. | M. obscura |
7. Bract margins toothed or lobed, or if entire, bracts green with white base. | → 14 |
14. Bracts green. | → 15 |
15. Styles 15–35 mm; stamens 11–40 mm, filaments heteromorphic, 5 outermost linear, inner filiform. | → 16 |
16. Petals usually elliptic to ovate, rarely obovate, 8–17(–21) mm wide; west slope of Sierra Nevada, California. | M. crocea |
16. Petals obovate, (12–)16–33 mm wide; Coast Ranges, California. | M. lindleyi |
15. Styles 2–15 mm; stamens 3–11 mm, filaments monomorphic, filiform. | → 17 |
17. Petals 3–7(–10) mm; styles 2–6 mm. | → 18 |
18. Petals red to orange proximally, orange to orange-yellow distally; styles (3–)3.5–6 mm. | M. veatchiana |
18. Petals orange proximally, yellow distally; styles usually less than 3.5 mm. | → 19 |
19. Bract margins 3-lobed or entire, lateral lobes never prominent; capsules 8–28(–35) mm (longest capsules usually more than 15 mm), axillary curved to 180°; 0–2300 m. | M. albicaulis |
19. Bract margins usually 3–7-lobed, rarely entire, lateral lobes usually prominent; capsules 6–17(–20) mm, axillary curved to 45°; 600–3400 m. | M. montana |
17. Petals 8–25 mm; styles 5–15 mm. | → 20 |
20. Petals yellow; bracts usually entire, rarely 2-lobed; w Mojave Desert, e Kern County, nw San Bernardino County, California. | M. eremophila |
20. Petals red to orange proximally, orange to yellow distally; bracts 3–7-lobed; s San Joaquin Valley, Inner Coast Ranges, s Sierra Nevada foothills, California. | → 21 |
21. Petals orange proximally, yellow distally; Fresno, Monterey, and San Benito counties, California, 200–1400 m, and s San Luis Obispo, Santa Barbara, and Ventura counties, California, 1500–1700 m. | M. gracilenta |
21. Petals red to orange proximally, orange to yellow distally; Kern, San Luis Obispo, Santa Barbara, and Tulare counties, California, 200–1400 m. | M. pectinata |
14. Bracts green with white base or mostly white with green margins. | → 22 |
22. Bracts concealing capsules, mostly white with green margins. | M. congesta |
22. Bracts not concealing capsules, green with white base. | → 23 |
23. Petals usually 8+ mm, usually orange, rarely yellow, proximally, yellow distally; seed coat cell outer periclinal wall domes on seed edges 1/2 as tall as wide at maturity. | → 24 |
24. Plants of grasslands, pine-oak woodlands; Coast and Transverse ranges, California. | M. gracilenta |
24. Plants of desert scrub, Joshua-tree woodlands; ne Los Angeles and w Riverside counties, California. | M. ravenii |
23. Petals usually less than 5 mm, red to orange proximally, orange to yellow distally; if petals 4+ mm, then seed coat cell outer periclinal wall domes on seed edges more than 1/2 as tall as wide at maturity. | → 25 |
25. Styles usually less than 3.5 mm. | → 26 |
26. Bracts 3–4.1 × 1.1–1.7 mm, margins entire; seeds not mottled, seed coat cell outer periclinal wall domes on seed edges less than 1/2 as tall as wide at maturity. | M. monoensis |
26. Bracts 5.9–9.2 × 1.7–5 margins usually 3–7-lobed, rarely entire,; seeds moderately to densely dark-mottled, seed coat cell outer periclinal wall domes on seed edges more than 1/2 as tall as wide. | M. montana |
25. Styles usually 3.5+ mm. | → 27 |
27. Petals red to orange proximally, orange to orange-yellow distally; bracts usually 3–7-lobed, rarely entire. | M. veatchiana |
27. Petals orange proximally, yellow distally; bracts 3–7-lobed or entire. | → 28 |
28. Plants of desert scrub, Joshua-tree woodlands; ne Los Angeles and w Riverside counties, California. | M. ravenii |
28. Plants of oak-pine woodlands, grasslands; Arizona, California, Nevada, Oregon. | M. veatchiana |
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