Muhlenbergia mexicana (Mexican Muhly)

Plant Info
Also known as: Satin Grass
Genus:Muhlenbergia
Family:Poaceae (Grass)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; average to moist soil; open woods, prairies, meadows, wetland edges, shores, gravel pits, roadsides, rock outcrops
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

[scan of panicles] Erect to somewhat nodding, slender branching clusters 1 to 8+ inches (2 to 21 cm) long at the top of the stem, arising from upper leaf axils and at the tips of branching stems. Lateral panicles are usually exposed, not hidden within the associated sheath. Several to many short-stalked to nearly stalkless spikelets (flower clusters) are overlapping on each branch, lance-elliptic in outline, 1.5 to 3.8 mm (to 3/16 inch) long, green to purplish, and have a single floret.

[close-up of spikelets] At the base of a spikelet is a pair of bracts (glumes), both 1-veined, hairless, pointed or short-awned at the tip, 1.5 to 3.7 mm long, about as long as or slightly shorter than the floret and the awn up to 2 mm long. Florets are surrounded by a pair of bracts (lemma and palea), both 1.5 to 3.8 mm long, narrowly lance-elliptic, the lemma 3-veined, pointed at the tip or with an awn up to 10 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 node, ligule and stem hairs] Leaves are alternate, 1 to 8 inches (2 to 20 cm) long, 2 to 6 mm wide, flat and hairless. Sheaths are hairless. The ligule (membrane where the leaf joins the sheath) is .4 to 1 mm long, jagged across the top and lacks a fringe of hairs. Nodes are smooth. Stems are slender, erect to ascending, much branched, minutely hairy for at least 4 mm below each node and hairless below that. Plants are not clump-forming, but can create colonies from elongated rhizomes.

Fruit: Fruit type: seed without plume

[photo of maturing spikelet and grain] Mature florets drop off individually leaving the glumes behind on the stalk. Grains (seeds) are 1.1 to 1.6 mm long, amber-colored to brown.

Notes:

Muhlenbergia is a rather variable genus: clusters spike-like or an open panicle; glumes and/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.

Mexican Muhly will grow pretty much anywhere, but has a preference for moist soil. Herbarium records put it in virtually every kind of habitat found in Minnesota: grasslands, wetlands, woodlands, rock outcrops, and frequently in the disturbed soils of roadsides, gravel pits and trail edges. Of the 10 Muhlenbergia species known to be in Minnesota, it is distinguished by the colony-forming and much branched habit, minutely hairy stems below the nodes, ligule less than 1 mm long, lateral panicles not usually tucked inside the sheaths, spikelet stalks mostly less than 2 mm long, both glumes and lemmas all near the same size (not counting awns), 1.5 to 3.8 mm long. There are 2 varieties, both of which are in Minnesota: var. filiformis has lemma awns 3 to 10 mm long; var. mexicana, the more common of the two, has awns less than 3 mm long or absent altogether.

Mexican Muhly can be confused with Wirestem Muhly (Muhlenbergia frondosa), which has hairless stems below the nodes, or minute hairs for not more than 4 mm, and stems tend to become sprawling later in the season, where Mexican Muhly stems remain erect to ascending. Also similar, but much less common, is Woodland Muhly (M. sylvatica), which is like Mexican Muhly in most respects except ligules are more than 1 mm long and spikelet stalks are mostly more than 2 mm long.

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More photos

Photos by K. Chayka taken in St. Louis County. Photos by Peter M. Dziuk taken in Renville County and in his garden.

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