Anthoxanthum (Group 6) might be keyed here if the pair of prominent, hairy, awned, dark brown sterile lemmas are not recognized as such. In Anthoxanthum, the spikelets are articulated above the glumes, unlike in Alopecurus, and the glumes are very unequal. Note also the comments on Phalaris under Crypsis.
1. Midrib of glumes prominently formed into a keel; glumes glabrous except for short cilia on the margins and veins; awns in the upper part of the inflorescence exceeding the lemmas by 4–5.5 mm, annual.
1. Midrib of glumes not formed into a keel; glumes usually at least sparsely pubescent between the veins, long-ciliate on the margins and veins; awns exserted beyond the lemmas 0–3.5 mm (to 6 mm in the tall, perennial A. pratensis).
2. Spikelets (excluding awns) ca. 4–6.5 mm long; awns mostly exserted ca. 3.5–6 mm beyond tips of glumes; anthers ca. 2.4–3.5 mm long.
2. Spikelets not over 3 mm long; awns at most exserted ca. 2–3 mm beyond tips of glumes; anthers less than 2 mm long.
3. Awn exserted at most about 1 mm beyond tips of glumes, usually included, inserted about a third or half the distance from base of lemma.
3. Awn of most lemmas exserted ca. 2–3 mm, inserted near the base of lemma (on lower 1/5–1/4).
4. Anthers 0.3–0.7 mm long; spikelets 2–2.5 mm long.
4. Anthers 1.4–1.8 mm long; larger spikelets 2.6–3 mm long.
All species found in Alopecurus
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 13, 2017. http://michiganflora.net/genus.aspx?id=Alopecurus.