Achnatherum hymenoides (Indian Rice Grass)
|Also known as:||Indian Mountain Ricegrass|
|Habitat:||sun; dry sandy or rocky soil; prairies, grasslands, dunes|
|Fruiting season:||July - August|
|Plant height:||10 to 28 inches|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Open, loose, branching cluster at the top of the stem, 2½ to 6 inches long, with 1 or 2 branches per node. Branches are up to 6 inches long, ascending to spreading, with 1 or more pairs of spikelets (flower clusters) per branch, each pair conspicuously forked with each spikelet on a wiry stalk up to 1 inch long. Spikelets are spindle-shaped in outline and have a single floret.
At the base of a spikelet is a pair of bracts (glumes), both about equal in size and shape, thin and papery, hairless to minutely hairy, 3-veined, 5 to 9 mm (to ~1/3 inch) long, narrowly egg-shaped with a long taper to a narrow tip, sometimes with an awn up to 2mm long. Florets are surrounded by a pair of bracts (lemma and palea), the lemma leathery becoming hardened, brown to black at maturity, densely white-hairy with mostly appressed hairs that easily rub off and are about as long as the lemma, the lemma body 3 to 4.5 mm long tapering to a straight or bent awn 3 to 6 mm long that falls off before maturity; the palea is similar to the lemma but lacks the awn.
Leaves and stems:
Leaves are mostly basal, about as long as the stem, very slender, .1 to 1 mm wide, rolled up along the edges (involute), smooth to slightly rough-textured, and stiff. The sheath is smooth to slightly rough-textured and sometimes minutely hairy along the edge near the tip. The ligule (membrane where the leaf joins the sheath) is 3 to 7.5 mm long, shorter on the upper stem, smooth to jagged along the tip and lacks a fringe of hairs. Nodes are smooth. Stems are unbranched, hairless, mostly erect, multiple from the base and forming loose to dense clumps.
Indian Rice Grass, formerly Oryzopsis hymenoides, is a common grass of the Great Plains and western North America from southern Canada to northern Mexico, but is extremely rare in Minnesota. According to the DNR, there are only a few known populations, all in the Agassiz Dunes complex that runs through Polk and Norman counties, and these are considered disjunct from western populations. While it may be found in many open, dry, well-drained habitats in the majority of its range, in Minnesota it is limited to sand dunes and blow-outs where competition is very limited. These are rare and fragile habitats, at risk from all manner of human activities and destructive land uses, as well as encroachment of woody species due to fire suppression. Indian Rice Grass was listed as a state Endangered species in 1984. It is a distinctive grass, recognized by its slender, involute, thread-like leaves, loose panicle of single-flowered, spindle-shaped spikelets, glumes longer than the floret, lemmas covered in long, white hairs that easily rub off, and lemma awns that drop off before maturity. And, of course, the pure sand habitat. Note that other references mention this is a densely clump-forming species, but the specimens we encountered were quite spindly.
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Photos by K. Chayka taken in Polk County. Photos courtesy Peter M. Dziuk taken in Polk County and in South Dakota.
Have you seen this plant in Minnesota, or have any other comments about it?