15. Agropyron repens (L.) Beauv. COUCH GRASS, QUACK GRASS.
A perennial with long running rootstocks which ramify through the soil and send up numerous shoots, forming a loose but tough sod; a grass of wide distribution and one of the weeds most difficult to eradicate from cultivated fields.
Leaves rolled in the bud-shoot. Sheath not compressed, not keeled, pubescent with soft, short, erect or retrorse hairs especially on lower leaves, rarely glabrous, green, split, with hyaline margins overlapping. Auricles present, 1 to 3 mm. long, slender, terete, clawlike, clasping. Collar distinct, puberulent both inside and outside, whitish, yellowish or sometimes purplish tinged, broad, V-shaped, divided by midrib, oblique. Ligule membranous, 0.5 to 1.0 mm. long, obtuse, finely tooth-fringed, ciliolate or entire. Blade 3 to 10 mm. wide, 8 to 20 cm. long, flat, slightly keeled at base, sharp-pointed, green sometimes slightly glaucous; upper surface generally sparsely pilose-pubescent, slightly ridged but midrib not conspicuous; margins and upper surface harsh-scabrous.
This grass is extremely variable in the degree of hairiness of the blades and sheaths. The hairs are more noticeable on the young leaves in the spring than on those formed later in the season. Agropyron repens may be distinguished from A. cristatum by its puberulent collar and less conspicuously ridged blade.