Lesser Yellow Rattle or Cockscomb does double duty as a very attractive plant to have in the meadow, but still more importantly it helps keep down the aggressive grasses like false oat grass, creating a better environment for a range of beautiful flowers like orchids to grow and increase.
The photos above are taken in early June at the bottom of ‘scrub’ field where the grassland had become rank and colonisation by brambles has started occurring, smothering the meadow flowers (see right-hand side of second photo). Since mowing away some of the rank vegetation last year, yellow rattle has started to grow again (middle foreground of second photo) keeping out the longer grasses (left-hand side) and creating a much shorter sward which will support a wider range of flowers.
This process has been looked at in great detail by wildlife managers – see here and here and here or here and here and is entirely due to yellow rattle’s unusual lifestyle. Essentially, it parasitizes on the roots of grass plants, sapping them of their energy and thus giving other plants a chance. Not popular with livestock farmers who demand a grassland barren of all except one or two grasses for their herd, but wonderful for wildlife and biodiversity!