Plants perennial, often flower-ing the first year. Culms 10–90 cm, sometimes decumbent and rooting at the lower nodes. Sheaths glabrous, smooth; ligules to 5 mm; blades 2–13 cm long, 1–6 mm wide. Panicles 2–10 cm, ovate-oblong to pyramidal, dense but inter-rupted, pale green to purplish; pedicels not developed; stipes 0.1–0.6 mm. Glumes 1.5–2 mm, scabrous on the back and keel, apices obtuse or truncate, unawned; lemmas about 1 mm, erose, unawned; paleas subequal to the lemmas; anthers 0.3–0.5 mm. 2n = 28, 42.

Polypogon viridis grows in mesic habitats associated with rivers, streams, and irrigation ditches. It is native from southern Europe to Pakistan, but is now established in the Flora region, particularly the southwestern United States. Records from the Atlantic coast are based on plants found on ballast dumps; there have been no recent collections from these locations. The record from Oregon is based on a misidentified specimens of Agrostis stolonifera. The map will be corrected eventually.

In Europe, Polypogon viridis hybridizes with P. monspeliensis, forming P. ×adscendens Guss. ex Bertol.; no such hybrids have been reported from the Flora region.