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Montana Field Guide

Montana Field Guides

Bractless blazingstar - Mentzelia nuda

Species of Concern
Native Species

Global Rank: G5
State Rank: S1S2
(see State Rank Reason below)

Agency Status
MNPS Threat Rank:

External Links

State Rank Reason (see State Rank above)
Rare and peripheral in Montana, where it is known from a few locations in the eastern half of the state. Additional data on population levels and trends are needed.
General Description
Bractless Mentzelia is an herbaceous biennial or short-lived perennial with one to a few erect, branched stems that arise from a taproot and are up to 1 m high. The lance-shaped, alternate leaves are 4-10 cm long, have deeply-toothed margins, and are petiolate below but sessile above. Foliage is covered with short, barbed hairs that cause it to stick to clothing like velcro. Flowers that open in late afternoon are borne on short stalks arising from the axils of reduced upper leaves, or bracts. Each flower is 4-9 cm across and has 10, non-overlapping, white petals and numerous exserted stamens. The calyx forms a deep bowl with 5 narrow, pointed lobes that are 10-25 mm long; it also contains the ovary and bears the stamens. The cylindrical seed capsules are 2-3 cm long.

Flowering in July.

Diagnostic Characteristics
Mentzelia decapetala has ten white petals, its larger flowers are 8-15 cm across, and its petals overlap.

Species Range
Montana Range


Range Comments
E. MT and SD south to CO, KS, and TX. Peripheral.

Observations in Montana Natural Heritage Program Database
Number of Observations: 14

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Sandy or gravelly soil of open hills and roadsides on the plains.

The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus centralis, Bombus fervidus, Bombus huntii, and Bombus pensylvanicus (Thorp et al. 1983, Williams et al. 2014).

  • Literature Cited AboveLegend:   View Online Publication
    • Thorp, R.W., D.S. Horning, and L.L. Dunning. 1983. Bumble bees and cuckoo bumble bees of California (Hymenoptera: Apidae). Bulletin of the California Insect Survey 23:1-79.
    • Williams, P., R. Thorp, L. Richardson, and S. Colla. 2014. Bumble Bees of North America. Princeton, NJ. Princeton University Press.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Brown, D. K. and R. B. Kaul. 1981. Floral structure and mechanism in Loasacae. American Jounal of Botany 68(3):361-372.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
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Citation for data on this website:
Bractless blazingstar — Mentzelia nuda.  Montana Field Guide.  .  Retrieved on , from