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Missoula County Oats - Trisetum orthochaetum
Other Names:  Trisetum x orthochaetum

Native Species

Global Rank: GNA
State Rank: SNA
(see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
Trisetum orthochaetum occurs only in Montana where it has been found in six locations: Lewis Range within Glacier National Park, near Lolo Hot Springs, and in the Granite Creek drainage within the Bitterroot Mountains. The Lolo Hot Springs location was extirpated by development in the 1950's. Work by Steve Shelly and L. H. Harvey concluded that the morphology is intermediate between T. canescens and T. wolfii which are also present where T. orthochaetum is collected. One study showed that seeds from T. orthochaetum are mostly sterile while the putative parents had mostly viable seeds. T. orthochaetum is presumed to be a hybrid that occurs on occasion but does not reproduce. Therefore, it is considered to be a hybrid without conservation value and is assigned the rank of SNA.
General Description
Stems few to a bunch, 80–110 cm tall; leaf blades 2–7 mm wide. Inflorescence a contracted and somewhat nodding panicle 13–20 cm long. Spikelets 7–9 mm long. Lemmas mostly 2 or 3, awns 4–6 mm long, straight, from upper half of lemma (Lavin in Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Trisetum orthochaetum flowers in July and spikelets persist into the first half of August (Shelly 1986).

Diagnostic Characteristics
In the Granite Creek drainage, Trisetum orthochaetum grows with its suspected parent species, T. canescens and T. wolfii. The lemma awns are useful for separating these taxa. T. orthochaetum has mostly straight awns that are 3-6 millimeters long, while T. wolfii lacks awns and T. canescens has longer (roughly 10-14 millimeter) awns that bend sharply when mature (Shelly 1986). Both T. orthochaetum and T. canescens have a ring of white hairs above the stem nodes, which T. wolfii lacks (Shelly 1986). In habitats where all 3 taxa are present, T. canescens is typical of relatively better-drained sites near the forest margin, T. wolfii is typical of wet meadows, and T. orthochaetum is generally found in intermediate microsites (Shelly 1986).

Range Comments
Currently known only from Glacier County and the Granite Creek Drainage, Missoula County (CPNWH 2017; Shelly 1986).

Observations in Montana Natural Heritage Program Database
Number of Observations: 7

(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)

Margins of montane moist meadows, often in the ecotone with adjacent coniferous forests (Shelly 1986).

Aphids were found on many of the inflorescences in one small population (Shelly 1986).

Reproductive Characteristics
Trisetum orthochaetum is thought to be a hybrid between T. canescens and T. wolfii. Its anthers seem to be non-functional. Chemical tests of germination with tetrazolium showed 0-3% of the seeds were viable. In contrast, tests of the suspected parent species indicated over 75% viable seeds (Shelly 1986). Additional research is needed to confirm the hybrid status of this species (Shelly 1986).

  • Literature Cited AboveLegend:   View Online Publication
    • Flora of North America Editorial Committee, eds. 2007. Flora of North America North of Mexico. Volume 24. Magnoliophyta: Commelinidae, Part 1. Oxford University Press, Inc., NY. xxxiii + 911 pp.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Shelly, J.S. 1986. Report on the conservation status of Trisetum orthochaetum, a candidate endangered species. Unpublished report. Montana Natural Heritage Program, Helena, MT 41 pp.
    • Shelly, J.S. 1987. Rediscovery and preliminary studies of Trisetum orthochaetum, Missoula County, Montana. Proceedings Montana Academy of Science 47:3-4 (Abstr.).
  • Additional ReferencesLegend:   View Online Publication
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    • Consortium of Pacific Northwest Herbaria (CPNWH) Specimen Database. No Date. Plant specimen data displayed on the PNW Herbaria portal. Website
    • Hitchcock, A. S. 1934. New species, and changes in nomenclature of grasses of the United States. Amer. J. Bot. 21:127-139.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
    • Lesica, P., P. Husby, and S. V. Cooper. 1998. Noteworthy collections: Montana. Madrono 45:328-330.
    • Watson, T. J. Jr. 1976. An evaluation of putatively threatened or endangered species from the Montana flora. Prepared for USDA Forest Service, Missoula, MT. 31 pp.
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Citation for data on this website:
Missoula County Oats — Trisetum orthochaetum.  Montana Field Guide.  .  Retrieved on , from