A tall Mediterranean grass, Sorghum halepense, now widely naturalized elsewhere and grown for fodder, but often regarded as a noxious weed.
Johnson grass/ˈdʒɒnsn ɡrɑːs/ /ˈdʒɒnsn ɡras/
Late 19th century. In some forms from the name of Col. William Johnson (fl. 1840), United States plantation owner, who was the first to grow the grass in large quantities in the United States + grass.