Achnatherum hymenoides (Indian Rice Grass)

Plant Info
Also known as: Indian Mountain Ricegrass
Genus:Achnatherum
Family:Poaceae (Grass)
Life cycle:perennial
Origin:native
Status:
  • State Endangered
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):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: irregular Cluster type: panicle

[photo of panicle] 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.

[photo of panicle branch] 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: Leaf attachment: alternate Leaf attachment: basal Leaf type: simple

[photo of wiry leaves] 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.

Fruit: Fruit type: seed without plume

[photo of mature spikelets, and floret with hairs rubbed off] The glumes become slightly spreading as each grain matures, the florets dropping off individually leaving the glumes behind on the stalk. Grains (seeds) are 2 to 3 mm long.

Notes:

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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More photos

Photos by K. Chayka taken in Polk County. Photos courtesy Peter M. Dziuk taken in Polk County and in South Dakota.

Comments

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

Posted by: Alexandra B - Minnetrista
on: 2017-08-30 11:10:52

along road side sandy soil near little long on game farm road

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