Muhlenbergia frondosa (Wirestem Muhly)

Plant Info
Also known as: Swamp Muhly
Family:Poaceae (Grass)
Life cycle:perennial
Habitat:part shade, shade; average to moist soil; woods, forest edges, floodplains, river banks, shores, ravines, wet meadows
Fruiting season:August - October
Plant height:1 to 3 feet
Wetland Indicator Status:GP: FACW MW: FACW NCNE: FACW
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle Cluster type: spike

[photo of panicles] Erect branching clusters 1 to 4 inches long at the top of the stem, arising from upper leaf axils and at the tips of branching stems. Lateral panicles are partially to mostly hidden within the associated sheath. Exposed panicle branches are initially ascending (spreading up to 30° from the stem), becoming more appressed with maturity. Several to many short-stalked spikelets (flower clusters) are overlapping on each branch, lance-elliptic in outline, 3 to 4 mm (to 1/6 inch) long, and have a single floret.

[close-up of panicle branch] At the base of a spikelet is a pair of bracts (glumes), both 1-veined, hairless, pointed or awned at the tip, the awn up to 4 mm long, the lower glume 2 to 4 mm long, the upper glume usually slightly longer, ¾ as long as to slightly longer than the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), both 2.2 to 4 mm long, narrowly lance-elliptic, the lemma 3-veined, pointed at the tip or with an awn up to 13 mm long; the palea is 2-veined, about as long as the lemma, pointed at the tip and awnless. The thickened base of the floret (callus) is covered in long, white hairs.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of sheath and ligule] Leaves are alternate, 1½ to 7 inches long, 1 to 7 mm wide, flat, smooth to slightly rough-textured, hairless, broadest near the middle and tapering slightly to the base, lacking a prominent collar (edge where the blade joins the sheath). Sheaths are hairless. The ligule (membrane where the leaf joins the sheath) is .5 to 1.5 mm long, jagged across the top, usually hairless but may have a sparse fringe of hairs. Nodes are smooth and shiny.

[photo of rhizomes] Stems are slender, much branched, hairless or rarely minutely hairy for 2 to 4 mm just below the nodes, initially erect to ascending becoming more sprawling later in the season, then rooting at the lower nodes. Plants are not clump-forming, but can create colonies from a tangled mass of thick, scaly rhizomes.

Fruit: Fruit type: seed_without_plume

[photo of mature spikelets (forma commutata)] Mature florets drop off individually leaving the glumes behind on the stalk. Grains (seeds) are 1.6 to 1.9 mm long, amber-colored to brown.


Muhlenbergia is a rather variable genus: clusters spike-like or an open panicle; glumes or lemmas awned, or neither; the callus (base of the floret) covered in long hairs or not; some with hairy stems or sheaths, others hairless; some branched, some not; clump forming or not; annual or perennial. What they have in common are spikelets usually single-flowered (occasionally with 2 or 3 florets), membranous ligules (occasionally also fringed with hairs), narrow leaves, glumes usually 1-veined, lemmas usually 3-veined, paleas 2-veined, and mature florets usually dropping off above the glumes (occasionally at the spikelet branch). There are about 70 species native to North America and more than 150 species worldwide.

Wirestem Muhly has been found in a variety of habitats but most often in shaded, moist places, often in disturbed soils, but may be found in open sites as well. Of the 10 Muhlenbergia species known to be in Minnesota, it is distinguished by the colony-forming and much branched habit, being essentially hairless throughout except for the callus, ligule .5 to 1.5 mm long, leaves to 7 mm wide and broadest near the middle, and lateral panicles at least partly tucked inside the sheaths. The spikelets are variable, however, with glumes longer or shorter than the floret and awned or not, lemmas awned or not, sometimes both awned and sometimes neither. Two forms are frequently noted: forma frondosa with lemma awns absent or under 4 mm long, and forma commutata with awns 4 mm or more long. Both may be present within a population.

Wirestem Muhly is most often confused with Mexican Muhly (Muhlenbergia mexicana), which more consistently has stem hairs below the nodes for more than 4 mm, and stems remain erect to ascending all season. Nimblewill (Muhlenbergia schreberi) is also similar in its sprawling growth, but lacks rhizomes, has a very short glume, hairless callus, a few long hairs at the tip of the sheath, and more slender spike-like panicles, none of which are hidden in the sheaths. While Wirestem Muhly is native and has some value as forage for both livestock and wildlife, it's been deemed an agricultural pest in some areas. Once established it can be difficult to manage, since it produces abundant seeds and rhizomes fragments can resprout. It is also a warm season grass so doesn't start growing with any vigor until long after herbicides are typically applied.

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More photos

Photos by Peter M. Dziuk taken in Itasca and Ramsey counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: gary - Carlton County
on: 2020-08-23 16:06:26

I think I may have found this grass today on my property. It doesn't key to M. mexicana but does key to M. frondosa.

Posted by: Aimee H Meyer - Minnetonka
on: 2021-08-31 10:03:28

This was a challenge to identify. A clump appeared in early August at the edge of my garden in Minnetonka.

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