Aristida basiramea (Forked Three-awn)

Plant Info
Also known as: Fork-tipped Three-awn, Base-branched Three-awn
Genus:Aristida
Family:Poaceae (Grass)
Life cycle:annual
Origin:native
Habitat:sun; dry sandy soil; prairies, roadsides, railroads, barrens, dunes
Fruiting season:August - October
Plant height:10 to 20 inches
Wetland Indicator Status:none
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: raceme

[photo of spikelet clusters] Loose, raceme-like branching cluster up to 4 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 to 3 spikelets (flower clusters) per branch. Spikelets are short-stalked, single-flowered, often purplish, the body 10 to 15 mm (~3/8 to ½ inch) long, narrowly lance-elliptic in outline.

[close-up of spikelet] 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 with a short awn (1 to 2 mm) extension, the lower glume body 7 to 11 mm long, the upper glume 9 to 12 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 8 to 9 mm long, mottled gray, narrowly lance-linear with a 3-branched awn at the tip, the central branch 9 to 15 mm long spirally coiled about 3 times at base, the lateral branches half to nearly as long and minimally coiled to merely angled at the base (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, up to 3 inches long, 1 to 1.5 mm wide, hairless, lance-linear, flat or folded towards the base and the edges usually rolled in (involute) towards the tip. 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. Stems are hairless, much branched at or near the base, stiffly erect, and forming loose clumps.

Fruit: Fruit type: seed without plume

[photo of dissected 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, 6 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 basiramea has the largest range and highest number of documented locations for Minnesota. However most of these records are over 50 years old and of the sites we have visited, none of them have high populations, not that some others don't.

A. basiramea is a wispy plant and easily overlooked, but is distinguished by its three awns, the central awn up to 15 mm (~½ inch) long, spirally coiled about 3 times at the base, and two lateral awns half to nearly as long, erect to spreading, loosely coiled once or twice or merely angled at the base. Its is most similar to Aristida longespica, which has awns that are all angled out but not coiled at the base. The awns of Aristida dichotoma are all much shorter, the central awn coiled but the two lateral awns much shorter, straight and erect from the top of the lemma. 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.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken in Anoka County.

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