Yellow rattle. Rhinanthus minor

Yellow-rattle is an annual that thrives in grasslands, living a semi-parasitic life by feeding off the nutrients in the roots of nearby grasses. For this reason, it was once seen as an indicator of poor grassland by farmers, but is now often used to turn improved grassland back to meadow - by feeding off the vigorous grasses, it eventually allows more delicate, traditional species to push their way through.