Definition of reed-grass in US English:

reed-grass

noun

  • The common reed, Phragmites australis; (also) any of various grasses, typically tall and growing in moist or wet soil, thought to resemble this; especially †(a) a cornfield grass, perhaps silky bent, Apera spica-venti (obsolete rare); (b) (more fully canary reed-grass) reed canary grass, Phalaris arundinacea; (c) a reed of the genus Calamagrostis, also called smallreed; (now chiefly US); (d) reed sweetgrass, Glyceria maxima.

Origin

Late 16th century (in an earlier sense). From reed + grass.