Aristida dichotoma (Churchmouse Three-awn)

Plant Info
Also known as: Poverty Grass, Poverty Three-awn, Shinner's Three-awn
Genus:Aristida
Family:Poaceae (Grass)
Life cycle:annual
Origin:native
Habitat:sun; dry sandy soil; prairies, open woods, roadsides, rock outcrops
Fruiting season:August - October
Plant height:10 to 20 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 Cluster type: raceme

[photo of spikelet cluster] Loose, raceme-like branching cluster up to 3½ inches long at the top of the stem, with smaller lateral clusters arising from leaf axils which are often at least partially enclosed in the leaf sheaths. Branches are mostly erect, with 1 or 2 spikelets (flower clusters) per branch. Spikelets are short-stalked, single-flowered, often purplish, the body 4 to 13 mm (1/6 to ½ inch) long, narrowly lance-elliptic in outline.

[photo of spikelet cluster] At the base of a spikelet is a pair of bracts (glumes), both thin and papery, hairless, 1-veined, narrowly lance-shaped tapering to a pointed tip, the lower glume 3 to 10 mm long, the upper glume 5 to 13 mm long and longer than the floret. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thicker than the glumes, 3-veined, the body 3 to 11 mm long, mottled gray to purplish, narrowly lance-linear with a 3-branched awn at the tip, the central branch 4 to 8 mm long spirally coiled about 3 times at base, the lateral branches much shorter (2 to 4 mm), straight and erect and reaching to about the tip of the upper glume (awns are all initially straight and twist with age); the palea is obscure and mostly enclosed by the lemma. The thickened base of the floret (callus) is covered in straight, white hairs.

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

[photo of ligule] Leaves are basal and alternate, widely spaced along the stem, up to 4¾ inches long, 1 to 2 mm wide, hairless, lance-linear, flat or folded. The sheath is loose, has thin, papery edging and is hairless or with sparse soft hairs. The ligule (membrane where the leaf joins the sheath) is fringed with short hairs less than 1 mm long. Nodes are smooth.

[photo of basal clump] Stems are hairless, branched at or near the base, stiffly erect, and forming tight clumps.

Fruit: Fruit type: seed without plume

[photo of mature spikelet] Spikelets are light brown at maturity, the florets shedding individually, leaving the glumes behind on the stalk. Grains (seeds) are chestnut brown, narrowly lance-linear, 5.5 to 7 mm long.

Notes:

The Aristida genus is a fairly large group of small to medium sized, clump forming grasses that are mostly associated with dry, sandy soils. They are commonly called three-awn grasses due to the three-parted awn at the tip of the lemma. Structurally there is a central and two lateral awns and the relative differences in length and degree of twisting of these awns is a primary diagnostic to their identification; many are readily distinguished on this characteristic alone, but the twisting may not be distinctive until maturity. There are six species found in Minnesota, and while three of the six are state listed as rare, from a field encounter perspective, the other three are relatively uncommon but for a few specific sites. Aristida dichotoma ranges west to east across the lower mid-section of Minnesota, but nearly all of the few collections in the state are restricted to rock outcrop habitats. However within those locations we've visited, we observed abundant populations.

A. dichotoma is distinct with a central awn loosely coiled at the base and two very short, erect lateral awns, and has the shortest awns of all the Minnesota Aristida species. It is most similar in form and awns to Aristida basiramea and Aristida longespica. The former has a central awn up to 15 mm long that is coiled at the base and lateral awns at least half as long that are loosely coiled or angled at the base. The latter has awns that are all more nearly equal in length and angled out but not coiled at the base. The awns of the other three Aristida species in Minnesota all have awns usually all about equal in size and 1 to several inches long.

There are two recognized varieties of A. dichotoma: var. dichotoma, present to our south and east and barely reaching into Wisconsin, has smaller spikelets with a central awn only 3 to 6 mm long, lateral awns only 1 mm long, and lemmas 3 to 8 mm long; var. curtissii, present in Minnesota, has a central awn 4 to 8 mm long, lateral awns up to 4 mm long, and lemmas 6 to 11 mm long.

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More photos

Photos by Peter M. Dziuk taken in Renville and Rock counties.

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