Avenula pubescens (Downy Oat Grass)
|Also known as:||Downy Alpine Oat-grass|
|Habitat:||sun; moist to dry; fields, roadsides, open woods, clearings|
|Fruiting season:||June - August|
|Plant height:||1 to 3 feet|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Loose, erect to nodding, branching cluster at the top of the stem, 4 to 7 inches long, the branches ascending to spreading at flowering becoming more erect in fruit. Branches have 1 to 4 spikelets (flower clusters), the upper branches mostly with single spikelets. Spikelets are short-stalked, 10 to 16 mm (~3/8 to 2/3 inch) long, slightly flattened, narrowly oblong-elliptic in outline and have 2 to 4 florets.
At the base of a spikelet is a pair of bracts (glumes), both thin and papery, hairless, keeled, elliptic with a pointed tip, the lower glume 7 to 13 mm (to ~½ inch) long and 1-veined, the upper glume 3-veined, slightly longer than the lower glume and about as long as or slightly shorter than the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thicker than the glumes, 5-veined, hairless, the body 9 to 14 mm long, notched and forming 2 pointed teeth at the tip with an awn arising from midway up the back, the awn 10 to 20 mm long and initially straight but becoming bent about the midpoint and spirally twisted on the lower half; the palea is somewhat shorter and narrower than the lemma. Arising from the base and running along the palea is a short stalk (rachilla extension), the tip of it and the thickened base of the floret both densely covered in white hairs up to 2.5 mm long.
Leaves and stems:
Leaves are basal and alternate but mostly near the base, erect to ascending, 1½ to 12 inches long, 2 to 6 mm (to ¼ inch) wide, lance-linear, flat or folded lengthwise, and whitish along the edges. Lower leaves are densely to moderately covered in fine, spreading hairs on both surfaces, upper leaves are usually hairless. The upper sheaths have overlapping edges and the lower sheaths are fused along the edge (closed) for part of their length. Like the leaves, lower sheaths are hairy and the upper hairless. The ligule (membrane where the leaf joins the sheath) is thin and not fringed with hairs, on lower sheaths up to 1 mm long and straight across, on upper sheaths 4 to 8 mm long and pointed at the tip. Nodes are smooth. Stems are hairless, usually multiple from the base, forming loose to dense clumps, and erect or sometimes prostrate from the base but rising at a lower node (genticulate).
Spikelets are light brown at maturity, the florets shedding individually as each grain matures, leaving the glumes behind on the stalk. Grains (seeds) are brown, narrowly elliptic, smooth with a few short hairs at the tip.
Downy Oat Grass, also known by synonym Helictotrichon pubescens, is a Eurasian introduction not known to be in Minnesota yet, but there is a well-established population in Ashland County, Wisconsin, and it's only a matter of time before it makes its way west. It is very similar to the rare native Spike Oat (Avenula hookeri), which has hairless leaves and stems, and to the more common Poverty Grass (Danthonia spicata), which has lemmas about half the size and the ligule is a fringe of long white hairs.
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Photos courtesy Peter M. Dziuk taken in Ashland County, Wisconsin.
Have you seen this plant in Minnesota, or have any other comments about it?