Setaria

1. Bristles, summit of culm, and axis of panicle scabrous with retrorse barbs; panicle branches tending to appear whorled, the panicle ± interrupted toward its base.

S. verticillata

1. Bristles, summit of culm, and axis of panicle scabrous or pubescent with antrorse barbs or hairs; panicle very compact throughout.

2. Fertile lemmas mostly ca. (2.7–) 3 (–3.4) mm long, rugose with distinctly transverse ridges, the upper half exposed at maturity; bristles 5 or more per spikelet, becoming orange or golden-brown; sheaths glabrous.

S. pumila

2. Fertile lemmas less than 3 mm long, evenly and finely rugose or reticulate or smooth (without transverse ridges), the upper half largely or entirely concealed at maturity; bristles fewer than 5 per spikelet, pale greenish or purple (rarely yellow) at maturity; sheaths ciliate with long hairs on the margins.

3. Spikelet articulated above the glumes and sterile lemma; fertile lemma distinctly yellow or darker at maturity; panicle very dense, often ± lobed in appearance.

S. italica

3. Spikelet articulated below the glumes; fertile lemma pale green or brown; panicle not lobed.

4. Panicle strongly nodding, bent below the middle; spikelets mostly over 2.5 mm long, the fertile lemma ± tapering to a distinctly exposed tip; leaf blades ± hairy above.

S. faberi

4. Panicle straight and erect or rarely slightly nodding; spikelets not over 2.5 mm long, the blunt fertile lemma nearly or quite concealed by the second glume; leaf blades glabrous above.

S. viridis

All species found in Setaria

Setaria faberiGIANT FOXTAIL 
Setaria italicaFOXTAIL, HUNGARIAN MILLET 
Setaria pumilaYELLOW FOXTAIL 
Setaria verticillataBRISTLY FOXTAIL 
Setaria viridisGREEN FOXTAIL 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. June 22, 2017. http://michiganflora.net/genus.aspx?id=Setaria.