Yellow Rattle or Hay Rattle (rhinanthus minor) is partly a parasitic species that draws some of its nutrients though the roots of grasses and is frequently used to increase bio diversity in wild flower meadows. Its parasitic nature suppresses the growth rate of grass, which in turn can make conditions more receptive for the establishment of other wildflower species. Used correctly it can reduce grass growth very successfully and once established can often spread to other areas within the meadow.