[taxon report][distribution map][all photos][line drawing]
Scientific Name: Mentzelia filifolia J. J. Schenk & L. Hufford
Vernacular Name: Threadleaf blazingstar
R-E-D Code: 2-1-2
Description: Biennial taprooted herbs, up to 7.5 dm tall; stem erect, straight, lateral branches on distal half of main stems at acute angles, straight; epidermis pubescent, becoming white, shedding with age; leaves alternate, rosette leaves unknown, cauline leaves 43–94(115) × 7.5–27(36) mm, rachis filiform, 1–2.4 mm wide, oblanceolate to elliptic in outline, pinnatisect with 8–20 filiform lobes, 6–12 mm apart, nearly opposite, perpendicular, regular, up to 3.2–17 mm long with acute apex, margins revolute, abaxial surface pubescence with greater density of simple grappling-hook, complex grappling-hook, and occasionally with needle-like trichomes than adaxial surface, adaxial surface with needle-like trichomes; inflorescence cymose, bract subtending inferior ovary entire to pinnate, 7–20 × 0.5–5.6 mm; calyx 6–11 × 1–3 mm, apices acute to attenuate, margins entire; petals five, yellow, glabrous, oblanceolate, 14–18.5 × 3.6–6 mm, apex acute; androecium yellow, stamens numerous, those of inner whorls shorter than outer whorls, filaments glabrous, anther epidermis not papillate, straight following dehiscence; outer whorl of stamens or staminodial and petaloid, oblanceolate, 10.3–14(18) × (1.4)2.5–4.4 mm, without anther, staminode apex acute; second whorl of stamens all fertile; ovary inferior, funnelform, 3 carpellate; style 10–12.5(14) mm long, stigmas 3; fruit a capsule, cylindrical, 11–19.3 × 5–7.5 mm, opening apically by three valves, base tapering; seeds grey to light brown, lenticular-ovoid, winged, 2.9–3.2 mm; testa reticulate, seed coat anticlinal cell walls sinuate, central papillae generally 42–48 per cell. Chromosome number: n = 10 (Thompson 3553 [US]). Flowers from July to September.
Similar Species: Mentzelia filifolia is distinguished from other similar Mentzelia species on the southeastern Colorado Plateau by its filiform leaf lobes and narrow leaf rachises. Specimens of M. filifolia were previously treated as M. laciniata. The two species are sympatric but M. laciniata has wider leaf rachises and lobes.
Distribution: Mentzelia filifolia is currently known from eastern Apache County, AZ and western McKinley County, NM. Collections have been made from the vicinity of Red Lake on the western flank of the Chuska Mountains, south to near Gallup, NM and Allentown, AZ south of I-40.
Habitat: Road cuts and shale slopes of the upper Chinle Fomation in piñon-juniper woodland at 1,850-2,300 m (6,400-7,500 ft) elevation.
Remarks: Currently known from only a few collections, this species may well be more locally common than indicated by the few herbarium specimens.
Conservation Considerations: The upper Chinle Formation is habitat for other rare plant species, including Erigeron sivinskii and the federally threatened Erigeron rhizomatus.
Important Literature (*Illustration):
*Schenk, J.J. and L. Hufford. 2011. Taxonomic novelties from western North America in Mentzelia section Bartonia (Loasaceae). Madroño 57:246-260.
Information Compiled By:
Andrea Hazelton, 2013