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Bank Haircap Moss - Polytrichastrum formosum
Other Names:  Polytrichum formosum

Native Species

Global Rank: G5
State Rank: SNR

Agency Status
MNPS Threat Rank:

External Links

General Description
Plants: Acrocarpous, growing in uncrowded clumps of erect shoots, deep blackish-green or olivaceous. Stems mostly 3-8 cm in height, rarely to 20 cm, borne from short, subterranean rhizomes (FNA 2007); rhizoids few, close to the base (Crum & Anderson et al., 1981).

Leaves: Upright or spreading to ca 45 degrees when dry, spreading more widely to nearly 90 degrees with the leaf apex broadly turned back and downward somewhat when damp, 6-12 mm in length, the sheathing base somewhat yellow with transparent, smooth margins, slowly narrowing to or suddenly constricted at the divergent blade with a distinct joint where the two meet; blade very slender to lance-shaped; margins with sharp teeth along the blade almost to the sheath; costa shortly extending beyond the apex, conspicuous and with teeth close to the apex on the dorsal leaf face (FNA 2007), the tip short and russet-colored (Crum & Anderson et al., 1981).

Leaf Cells: Marginal lamina 2-10 cells in width, flat or upright (“holding in” the lamellae), the marginal teeth of the blade each consisting of 1 long cell (FNA 2007); lamellae 22-58, green, nearly completely obscuring the ventral leaf surface from shoulder to leaf tip (Crum & Anderson et al., 1981), from a side-view appearing like a wall of cells that are smooth to finely toothed along the top and 3-7 cells in height, the topmost (marginal) lamellar cell in X-section somewhat oblong and greater in height than the underlying cells; sheath cells quadrangular and slender; costa in X-section with large guide cells and a dorsal stereid band (FNA 2007).

Range Comments
North American Range

Canada: NT, BC, MB to NL and NS; USA: WA, CA, CO, MN and WI, TN, PA ne to ME (FNA 2007). Known in Montana from Beaverhead, Gallatin, Glacier, Lake, and Missoula Counties (Elliott & Pipp, 2016).

Observations in Montana Natural Heritage Program Database
Number of Observations: 2

(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)

Damp humus and soil in evergreen woods, bogs (Crum & Anderson et al., 1981).

Reproductive Characteristics
Dioicous or polygamous. Perichaetial bracts a little longer but otherwise resembling stem leaves. Seta single, 3-6 cm in height, brown with yellow tones, or russet. Capsule ochre or more brownish, 3-6 mm in length, with 4 or seldom 6 rather sharp angles (FNA 2007), the theca 3.5-7 mm in length (Lawton 1971), the neck with no clear beginning or occasionally bounded with a slight groove; peristome with 64 mostly even teeth or not so many and somewhat varying (FNA 2007), the teeth with tiny papillae (Lawton 1971). Calyptra sheltering the upper part of the capsule, draping like a hood and covered with matted hairs (polytrichoid) (FNA 2007).

  • Literature Cited AboveLegend:   View Online Publication
    • Crum, H.A. and L.E. Anderson. 1981. Mosses of Eastern North America. 2 volumes. Columbia University Press, New York. 1328 pp.
    • Elliott, J.C. and A.K. Pipp. 2018. A Checklist of Montana Mosses (1880-2018). Updated 3 January, 2020. Montana Natural Heritage Program, Helena, Montana. 73 pp.
    • Flora of North America Editorial Committee, eds. 2007. Flora of North America North of Mexico. Volume 27. Bryophytes: Mosses, Part 1. Oxford University Press, Inc., NY. xxi + 713 pp.
    • Lawton, E. 1971. Moss Flora of the Pacific Northwest. Hattori Botanical Laboratory. Japan: Yamabuki-cho, Shinjuku-ku, Tokyo. 362 pages plus appendices.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Lawton, E. 1971. Keys for the Identification of the Mosses on the Pacific Northwest. Reprinted from 'Moss Flora of the Pacific Northwest'. Published as Supplement No. 2 of the Journal of the Hattori Botanical Laboratory. Nichinan, Miyazaki, Japan. 66 pp.
    • Malcolm, B., N. Malcolm, J. Shevock, and D. Norris. 2009. California Mosses. Nelson, New Zealand: Micro-Optics Press. 430 pp.
    • Smith, A.J.E. 1980. The Moss Flora of Britain and Ireland. Cambridge University Press, Cambridge. 705 pp.
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Citation for data on this website:
Bank Haircap Moss — Polytrichastrum formosum.  Montana Field Guide.  .  Retrieved on , from