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Montana Field Guides

A Dry Rock Moss - Grimmia longirostris
Other Names:  A Black Rock Moss, Grimmia affinis

Native Species

Global Rank: G5
State Rank: SNR

Agency Status
MNPS Threat Rank:

External Links

General Description
Plants: Compact cushions. Yellow-green to dark olivaceous. Stems 1-3 cm tall. In X-S the stem has a strong central strand.

Leaves: Ovate-lanceolate, 1.5-3.0 x 0.6-0.7 mm, and keeled. Awn 0.5-1.5 mm long, broadly attached and decurrent. One margin proximally recurved. Costa reaches apex.

Leaf Cells: Basal laminal cells near costa are long-rectangular to linear, sinuose, and thick-walled. Basal laminal cells near margin are short-rectangular, straight, thick-walled transversely, thin-walled laterally, and hyaline. Median laminal cells are short-rectangular, sinuose, and thick-walled. X-S: distal laminal and marginal cells are 2-layered and not bulging. Costa X-S: Reniform in outline (keeled).

Diagnostic Characteristics
Grimmia affinis has frequently been considered a subspecies of G. ovalis. However, G. affinis is autoicous, and its leaves have one recurved margin which are keeled narrowly near the tip. G. ovalis, on the hand, is dioicous and has flat leaf margins that are widely concave above (FNA 2007).

Range Comments
Rocky Mountains from New Mexico to the southern Canadian provinces, extending east in the U.S. to Minnesota. Greenland; Canada: AB, BC, MB, NB, NL, NT, NS, NU, ON, QC, SK, YT; USA: AK, AZ, CA, CO, ID, ME, MN, MT, NV, NH, NM, NC, OK, OR, SD, TX, UT, VT, WA, WY; Mexico; Central America; South America; Eurasia; Africa; Pacific Islands; Australia (FNA 20007). In Montana, known from Carbon, Flathead, Glacier, Gallatin, Madison, Mineral, and Missoula Counties (Elliott 2016).

Exposed, dry, acidic granite and quartzite rock. Low to moderate elevations (330 – 10,200 feet). It is common on the eastern side of the Rocky Mountains.

Reproductive Characteristics
Seta is 1.0-4.0 mm tall, straight, and centrally attached to capsule. Capsules are often found, usually exserted (sometimes emergent), yellow, oblong-ovoid to cylindric. Autoicous.

Gemmae absent on leaves.

  • Literature Cited AboveLegend:   View Online Publication
    • Elliott, J.C. and A.K. Pipp. 2018. A Checklist of Montana Mosses (1880-2018). December 20th. Montana Natural Heritage Program, Helena, Montana. 73 pp.
  • 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.
    • Lawton, E. 1971. Moss Flora of the Pacific Northwest. Hattori Botanical Laboratory. Japan: Yamabuki-cho, Shinjuku-ku, Tokyo. 362 pages plus appendices.
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Citation for data on this website:
A Dry Rock Moss — Grimmia longirostris.  Montana Field Guide.  .  Retrieved on , from