Setaria faberi R. A. W. Herrm.
Giant foxtail (Darbyshire 2003; AOSA 2024)
Chinese foxtail (Barkworth et al. 2003)
Japanese bristlegrass (USDA-NRCS 2024)
Nodding bristle grass (USDA-ARS 2024)

• Spikelets of S. faberi are usually 2.5 to 3 mm long (Barkworth et al. 2003), somewhat pointed at the tip, and distinctly humped in profile view, whereas S. viridis spikelets are usually smaller (less than 2.5 mm long), more broadly angled at the tip, and flatter in profile view.
• The upper (2nd) glume in S. faberi is three-quarters the length of the spikelet or less and the upper portion of the fertile lemma is exposed, while in S. viridis the upper glume is nearly the same length as the spikelet and completely conceals the fertile lemma.
• The tuberculate texture of the fertile floret lemma in S. faberi is transversely ridged in the lower two-thirds, whereas in S. viridis it is not ridged.

Setaria italica (L.) P. Beauv.
Foxtail millet (Barkworth et al. 2003; AOSA 2024; USDA-NRCS 2024)
Italian millet (AOSA 2024)

• The spikelets of S. italica tend to be longer and wider (2 – 3 mm long; 1.5 mm wide; Musil 1963; Barkworth et al. 2003) than those of S. viridis (2.1 – 2.4 mm long; 1.1 – 1.3 mm wide).
• The upper (2nd) glume is only about three-quarters the length of the spikelet in S. italica, whereas in S. viridis the upper glume is nearly equal in length to the spikelet (Musil 1963).
• The fertile floret in S. italica can be light yellow to dark golden yellow, orange, or purplish-brown depending on the variety and the lemma nerves are inconspicuous, while in S. viridis the fertile floret is greenish-yellow to light brown, often with darker brown mottling and the lemma nerves are lighter in color.
• In S. italica the fertile florets fall from the plant leaving the glumes, sterile floret, and subtending bristles attached to the plant, whereas in S. viridis the entire spikelet falls as a unit from the plant (CABI 2021).

Setaria parviflora (Poir.) Kerguélen
Knotroot bristlegrass (AOSA 2024)
Knotroot foxtail (Wiersema and León 1999)
Marsh bristlegrass (USDA-NRCS 2024)
Slender pigeon grass (ALA 2024)

• The spikelets of S. parviflora can be slightly longer (2 – 2.8 mm; Barkworth et al. 2003), compared to S. viridis (2.1 – 2.4 mm), but are similar in width (1.1 – 1.3 mm wide) (Walters 2011).
• In S. parviflora the upper (2nd) glume is one-half to two-thirds the length of the spikelet and the upper portion of the fertile lemma is exposed, while in S. viridis the fertile lemma is concealed by the upper glume.
• The fertile floret lemma in S. parviflora is pointed, while it is broadly angled (obtuse) in S. viridis.
• The fertile lemma in S. parviflora is transversely ridged, while in S. viridis it is not ridged.
• The glossy margins of the fertile palea are concealed by the in-rolled lemma margins in S. parviflora, whereas in S. viridis the glossy palea margins are exposed.

Setaria pumila (Poir.) Roem. & Schult. subsp. pumila
Yellow foxtail (AOSA 2024; USDA-NRCS 2024)
Yellow bristlegrass (AOSA 2024)
Pale pigeon grass (ALA 2024)

• Spikelets of S. pumila subsp. pumila are generally larger (2 – 3.5 mm long; Barkworth et al. 2003; eFloras 2024) and distinctly humped in profile view, whereas S. viridis spikelets are usually smaller (less than 2.5 mm long) and flatter in profile view.
• The upper (2nd) glume in S. pumila subsp. pumila is about one-half the length of the spikelet and the upper portion of the fertile lemma is exposed, while in S. viridis the upper glume is nearly the same length as the spikelet and completely conceals the fertile lemma.
• The fertile floret lemma in S. pumila subsp. pumila is transversely ridged, while in S. viridis it is not ridged.
• The glossy margins of the fertile floret palea are concealed by the strongly in-rolled lemma margins in S. pumila subsp. pumila, whereas in S. viridis the glossy palea margins are exposed.

Setaria verticillata (L.) P. Beauv.
Hooked bristlegrass (Barkworth et al. 2003; USDA-NRCS 2024)
Bur bristlegrass (AOSA 2024)
Bristly foxtail (DiTomaso and Healy 2007).
Whorled pigeon grass (ALA 2024)

• Spikelets of S. verticillata are similar in size and shape to those of S. viridis and are considered indistinguishable (Musil 1963). The tips of the spikelet and fertile floret lemma in S. verticillata are slightly more pointed than in S. viridis (Walters 2011), but this is not a reliable distinction.
• The bristles subtending each spikelet in S. verticillata are retrorsely barbed (barbs downward pointing), hence the common names of hooked or bur bristlegrass because the bristles tend to catch on clothing or fur, as opposed to the antrorsely barbed bristles (barbs pointing toward bristle tip) subtending each spikelet in S. viridis that do not stick to clothing or fur (Barkworth et al. 2003; DiTomaso and Healy 2007; CABI 2024).