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Mat Prickly-phlox - Leptodactylon caespitosum
Other Names:  Linanthus caespitosus, Linanthus cespitosus

Species of Concern
Native Species

Global Rank: G4
State Rank: S2S3
(see State Rank Reason below)

Agency Status
MNPS Threat Rank: 3

External Links

State Rank Reason (see State Rank above)
This plant occurs in Montana at the edge of a broad but patchy range. It is known from only a dozen or so mostly small populations, all in the Pryor Mountains - Bighorn Canyon area, and is confined to a very specific substrate. The habitat of this plant receives little human disturbance and there are no evident threats.
  • Details on Status Ranking and Review
    Mat Prickly-phlox (Leptodactylon caespitosum) Conservation Status Review
    Review Date = 05/29/2013
    View State Conservation Rank Criteria
    Population Size

    Score2 - Small: Generally 2,000-10,000 individuals.

    Range Extent

    Score3 - Local Endemic or Very Small Montana Range: Generally restricted to an area <10,000 sq. miles (equivalent to the combined area of Phillips and Valley Counties) or <6 Sub-basins (4th code watersheds) Range-wide OR limited to one Sub-basin in Montana

    Area of Occupancy

    Score2 - Low: Generally occurring in 4-10 Subwatersheds (6th Code HUC’s).

    Environmental Specificity

    Score1-2 - Moderate to High.

    CommentPrimarily confined to Chugwater Sandstone.


    ScoreNA - Rank factor not assessed.


    Score0-1 - Low to Medium.

    CommentNo specific threats have been identified.

    Intrinsic Vulnerability

    Score0-1 - Low to Moderate Vulnerability.

    CommentDoes not appear to be especially vulnerable as a result of any biological factors.

    Raw Conservation Status Score

    Score 8 to 11 total points scored out of a possible 16 (Rarity factors and threats only).

General Description
Leptodactylon is a cushion-forming perennial with a highly branched rootcrown that gives rise to numerous herbaceous stems that are up to 2 cm high. Each stem is closely covered by opposite, deeply 2-3 equally-lobed, spine-tipped leaves that are 3-6 mm long. The foliage is glabrous to glandular. Solitary flowers are borne on the stem tips. The pinkish-white, tubular corolla is 12-20 mm long and flares into 4 spreading lobes. 4 anthers are borne near the top of the tube, and the calyx is 5-8 mm long with 4 shallow, pointed lobes. The fruit is a round capsule.

Flowering occurs in May-June, and capsules ripen in June.

Diagnostic Characteristics
In Montana, Leptodactylon caespitosum is only known to occur on the Chugwater formation of the Pryor Mountains. Species of the closely related genus Phlox (e.g., P. bryoides, P. hoodii) also form low-growing mats, but have a 5-lobed corolla and a 5-parted calyx.

Species Range

Range Comments
Carbon County; MT south to NV, UT, WY and NE (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 40

(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)

The species is restricted in Montana to foothills of the Pryor Mountains, where it is typically found on north- or east-facing slopes in dry, open sandy breaks confined to outcroppings of Chugwater sandstone -- an unusual though locally common substrate (Lesica and Achuff 1992). Its sparsely vegetated habitat is dominated by Juniperus osteosperma and Agropyron spicatum, with occasional Pinus flexilis. Common associates include Phlox muscoides, Chrysothamnus nauseosus, Mentzelia pumila, Eriogonum lagopus, Wyethia scabra, Astragalus hyalinus, and Cryptantha cana.

Ecological Systems Associated with this Species

This plant grows in harsh, sparsely vegetated habitats where there is limited competition from other species. It appears to be confined to calcareous soils (Cronquist et al. 1984, Welsh et al. 1993). In Montana it is restricted to Chugwater sandstone that is interbedded with gypsum. Over half of the populations surveyed in 1992 had fewer than 100 plants.

Given its low growth form, this plant is probably little impacted by livestock grazing. At one population, livestock had trailed through it with no evidence of plant mortality.

  • Additional ReferencesLegend:   View Online Publication
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    • Cronquist, A., A.H. Holmgren, N.H. Holmgren, J.L. Reveal, and P.K. Holmgren. 1984. Intermountain Flora: Vascular Plants of the Intermountain West, U.S.A. Vol. 4, Subclass Asteridae (except Asteraceae). Bronx, NY: New York Botanical Garden. 573 pp.
    • Lesica, P. and P.L. Achuff. 1992. Distribution of vascular plant species of special concern and limited distribution in the Pryor Mountain desert, Carbon County, Montana. Unpublished report to the Bureau of Land Management. Montana Natural Heritage Program, Helena, MT. 105 pp.
    • Lesica, P., M. T. Lavin, and P. F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Welsh, S.L, N.D. Atwood, S. Goodrich, and L.C. Higgins. 1993. A Utah Flora, second edition, revised. Brigham Young University, Provo, UT.
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Mat Prickly-phlox — Leptodactylon caespitosum.  Montana Field Guide.  .  Retrieved on , from