What is the name of the moorland plant that serves as a significant food source for grouse?

Heather is a crucial moorland plant for grouse, particularly in the context of the British countryside. It provides not only shelter but also a vital food source for various species of grouse, such as red grouse. The plant's leaves and young shoots are nutritious and are an essential part of the grouse's diet, especially during critical periods when other food sources may be scarce. Heather thrives in acidic soils and is well-suited to the moorland environment, creating extensive fields that support healthy populations of grouse.

The other options, while they may exist in moorland habitats, do not provide the same level of sustenance for grouse as heather does. Bramble, for example, primarily offers protection and berries that might be consumed opportunistically by grouse, but it is not the primary food source. Thistles and ferns do not play a significant role in the diet of grouse, making heather the standout choice for this question.