Alpine Bentgrass - Podagrostis humilis
Agrostis humilis, Agrostis thurberiana, Podagrostis thurberiana
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There are numerous collections of Podagrostis humilis from 1926 to 2016 that come from the western-third of Montana. Most collections were documented after 1979. Podagrostis humilis is a wide-ranging (circumboreal) grass that grows in subalpine and alpine habitats that appear to be secure.
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Plants: Perennial bunchgrass, but occasionally plants have short rhizomes (Lesica 2012). Stems usually 7-15 cm tall, but can be up to 50 cm (Lesica 2012). Their base sometimes is decumbent.
Leaves: Mostly basal, 2-15 cm long and 0.5-1.0 mm wide (Lesica 2012; FNA 2007). Blades are flat or involute (FNA 2007). Ligules are 0.5-2.7(4.0?) mm long, scabrid, truncate to obtuse, and usually erose to lacerate though sometimes entire (Lesica 2012; FNA 2007).
Inflorescence: Contracted panicle of usually 1–3 (sometimes to 5) cm length (Lesica 2012), sometimes drooping (FNA 2007). The lowest panicle nodes have 1-4 branches (FNA 2007). Spikelets are ovate to lanceolate, green to purple, and 1.7–2.0 mm long (Lesica 2012; FNA 2007). Glumes are less than 2.3 mm long with acute tips (FNA 2007). The lower glume is equal to or longer than the upper glume (FNA 2007). Palea is 0.9 – 1.6 mm long, about two-thirds as long as the lemma (Lesica 2012; FNA 2007). The lemma is 1.7–1.9 (to 2.3) mm long, usually not awned but sometimes with a short-awn (Lesica 2012; FNA 2007). The rachilla extends (prolongs) 0.1-0.6 mm beyond the floret, with a tuft of short hairs at the apex (FNA 2007).
Podagrostis has been separated from Agrostis based on a combination of having a relatively long palea and a rachilla that extends beyond the base of the floret (FNA 2007). Podagrostis grasses grow in cool, wet areas (FNA 2007).
This treatment follows the Flora of North America, Volume 24, for Podagrostis humilis and includes Podagrostis thurberiana (Hitchc.) Hulten (formerly Agrostis thurberiana A.S. Hitchcock). Podagrostis thurberiana differs in having a larger, more open panicle and having wider leaves (FNA 2007). Podagrostis thurberiana is also taller (up to 50 cm) and grows in the mountains below the subalpine zones (Lesica 2012). However, characteristics form a continuum between the extreme forms and don’t deserve merit at the species level (FNA 2007).
In comparison to Calamagrostis, Podagrostis species lack developed callus hairs and awned lemmas.
Throughout western North America and sporadically elsewhere (Lavin in Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Observations in Montana Natural Heritage Program Database
Number of Observations:
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(Observations spanning multiple months or years are excluded from time charts)
Undisturbed alpine and subalpine meadows, screes, or dry mountain meadows at lower elevations (Lesica 2012; FNA 2007). However, specimens have been collected near campgrounds and in a mine.
- Literature Cited AboveLegend: View Online Publication
- Flora of North America Editorial Committee. 2007. Flora of North America North of Mexico. Vol. 24. Magnoliophyta: Commelinidae (in part): Poaceae, part 1. Oxford Univ. Press, New York. xxviii + 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.