Aristida

Except for A. purpurascens, the species are all quite uncommon in Michigan and all are at the edge of their range in the state. Our plants are fairly easily distinguished, but the measurements in the key may fail completely to apply to forms of the same species farther south and west, where there is apparently much more overlapping of characters and even greater variability in size of awns, glumes, and lemmas. Great Lakes area populations generally need more study.

1. Awns tightly twisted and ± connate, forming a column ca. 5–9 mm long at summit of lemma before diverging into 3 ± equal and much longer free portions.

A. tuberculosa

1. Awns not forming a column, separate from their bases.

2. First glume with 3–5 distinct nerves, ca. 16–24 mm long (plus awn if present); body of lemma ca. (12–) 15–17 (–21) mm long; awns ca. 3.5–6 (–7.5) cm long.

A. oligantha

2. First glume with 1 distinct nerve, 2.5–12.5 mm long; body of lemma 3.5–11 mm long; awns less than 3.5 cm long.

3. Middle awn on most lemmas loosely spiraled (at least when dry) in 1 or 2 loops toward its base.

4. Body of lemma ca. 7–11 mm long, with middle awn 9–18 mm long and lateral awns 6–12 mm long; glumes clearly unequal, the first usually equaling or shorter than the body of the lemma.

A. basiramea

4. Body of lemma ca. 5–7 mm long, with middle awn mostly 4–8 mm long and lateral awns less than 2 mm long; glumes mostly subequal, both longer than body of lemma.

A. dichotoma

3. Middle awn on most lemmas bent, slightly twisted, or straight, without spiraled loops at base.

5. Middle awn of lemma ca. 7–12 mm long, strongly divergent or somewhat reflexed; lateral awns 1–4 (–5) mm long, ± erect or slightly spreading; first glume 2.5–4 (–6) mm long (excluding awn-tip if present); body of lemma ca. 3.5–5.5 mm long.

A. longespica

5. Middle awn of lemma ca. 15–33 mm long; lateral awns ca. 9–26 mm long; all awns somewhat spreading or divergent; first glume (4–) 5–12.5 mm long; body of lemma ca. 5–8 mm long.

6. First glume ca. (4–) 5–8 (–8.5) mm long, slightly shorter than second glume; lower sheaths essentially glabrous, the nodes mostly exposed; plants annual.

A. necopina

6. First glume (8–) 8.5–13.5 mm long, slightly longer than second glume; lower sheaths usually ± pilose, covering the nodes; plants perennial.

A. purpurascens

All species found in Aristida

Aristida basirameaFORK-TIPPED THREE-AWNED GRASS 
Aristida dichotomaPOVERTY GRASS 
Aristida longespicaTHREE-AWNED GRASS 
Aristida necopinaTHREE-AWNED GRASS 
Aristida oliganthaPLAINS THREE-AWNED GRASS 
Aristida purpurascensTHREE-AWNED GRASS 
Aristida tuberculosaBEACH THREE-AWNED GRASS 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. May 25, 2017. http://michiganflora.net/genus.aspx?id=Aristida.