pearl grass
/ˈpəːl ɡrɑːs/ /ˈpəːl ɡras/(also pirl grass, purl grass)
noun
1The large quaking grass, Briza maxima, especially a variety with albino spikelets, grown for ornament.
2The onion couch, Arrhenatherum elatius var. bulbosum. Also (occasionally): the common couch grass, Elymus repens.
Origin
Mid 17th century; earliest use found in Thomas Johnson (d. 1644), apothecary and soldier. From pearl + grass.