5a. var. ambigua (Guss.) Parl.

Leaf sheaths with the ligule 1.0–2.2 mm long. Leaf blades roughened on both surfaces, often also with sparse longer hairs on the upper surface. Bristles subtending the spikelets roughened with short, upwardly pointing hairs. June–October.

Introduced, known only from St. Louis (native of Europe; introduced and weedy nearly worldwide). Railroads.