This non-native invader didn’t arrive the way legend suggests. According to lore, a Spanish friar, traveling between the missions, planted mustard seeds along the way, marking El Camino Real with yellow flowers. It’s a romantic notion, but unlikely. Neither were the seeds planted to feed cattle. Cattle dislike these varieties of mustard. More likely, the missionaries grew it for its oil, if not for culinary purposes, and it quickly spread out of control. As early as 1827, Capt. José María Estudillo, reporting on Mission San Juan Capistrano, wrote that mustard made most of the land useless and that “there is so much of it that it cannot be destroyed by human means.” Today, it still strangles native plants. Mustard tastes good on hot dogs, but it’s an invasive species California must battle.