This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
No type of natural vegetation, perhaps, exhibits so marked a habit of growth on a wide scale as ericetal vegetation.
The most obvious character in open association, where trees are absent, is the dwarfing of the vegetation. This is due not only to the necessity of a reduction of parts such as leaves, etc, and a certain stem habit, but also to the need for meeting the exposure to the wind. An inland heath in this respect is similar to the vegetation of the sea-coast where wind plays a constant and important part. The type of growth is typically ericoid, as in the heath plants, with whorls of linear, erect leaves, and fastigiate or closely grouped branches, developed much on the lines of the tufted foliage and stems of grasses. Owing to this close habit of the dominant types of heath plants other plants have to adapt themselves accordingly, and even where Ling, etc, is discontinuous, and where there is an alteration of conditions, there are few types except the grass type. But amongst the heath types a few others manage to survive in locally open spots, and these have usually the trailing habit, or else they have the erect rigid habit of St. John's Wort, with few branches and short, not very broad, leaves. Some are rosette plants, as Hawkweeds, Sheep's-bit Scabious. Here and there on rocks or ledges plants having a mat'or cushion habit occur. Many others have a sort of grass habit, as Harebell, Cow-wheat, etc.