Yellow rattle or hay rattle - Rhinanthus minor is one of the most intriguing plants of hay meadows. It is semi-parasitic on the roots of grasses and where it is abundant it can appreciably suppress grass growth. For this reason, in the past when productivity of hay meadows was so important, yellow rattle was not favoured as it reduced hay yield.
Unusually for a grassland plant, it is an annual – totally dependent on setting seed each year to survive. It quickly sets masses of seed in June – seemingly perfectly timed to precede the hay cut!
The seed is held in the ‘balloon’ like sepals and as these dry out and the seed ripens, so the cases ‘rattle’ and the seed is shaken out in the breeze. Hay-turning also helps scatter and spread the seed.
Yellow rattle’s life style is well adapted to the hay meadow yearly cycle – so conserving hay meadows is key to this plant’s survival.