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.
On the typically dry acid peaty soil, in the lowlands of England especially, the dry heath is characterized by the predominance of the Heather or Ling, Hell Heather, and in some parts by Cross-leaved Heath and Cornish Heath. The Whortleberry is also a common constituent. These plants form wide associations, and make up a large proportion of the vegetation altogether. But with them may also be found Milkwort, Pretty St. John's Wort, Purging Flax, Broom, Furze, Tormentil, Heath Bedstraw, Saw Wort, Harebell, Dodder, Red Rattle, Eyebright, Cow Wheat, Wood Sage, Juniper, various Sedges (e.g. Early Sedge), Bent Grasses, Matweed, Purple Hair Grass, etc.
The wet heath developed in hollows, where water lies, may closely resemble the moor, and the peat is then usually thicker. In such places may be found Marsh Violet, Sundew, Cranberry, Ling, Cross-leaved Heath, Butter-wort, Lesser Skullcap, Gentian, Creeping Willow, Sweet Gale, Bog Orchid, Heath Rush, Spike Rushes, Bulrush, Cotton Grass, Beak Sedge, Flea Sedge, Purple Hair Grass, Matweed, Royal Fern, Club Moss, and Bog Mosses.