arrowgrass
(ˈærəʊˌɡrɑːs) n (Plants) either of two species, sea arrowgrass (Triglochin maritima) or marsh arrowgrass (T. palustris), of monocotyledonous perennials having long thin fleshy leaves and spikes of inconspicuous flowers
[C18: named from the shape of the fruits when open]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014