This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Owing to the differences in temperature, effect of wind, etc, between the lowland and upland regions, there are several types of plant groups which may be distinguished as montane or descending and lowland or ascending. The montane plants are as a rule of wider range in the northern regions, and the lowland plants more widespread in the south.
The montane plants include, first of all, eu-montane species, chiefly of Arctic type, as the Cloudberry. They seldom descend below the Infer-Arctic Zone, or about 1800 ft., where the temperature is 390 F. to 420 F. In Britain the eu-montane group ranges between 2000 ft. and 3200 ft. The general montane group is found at altitudes between 2000 ft. and 1000 ft., and is most common in the north generally speaking, as Juniper, Whortleberry, Cowberry, etc. The sub-montane group is found at altitudes between 500 ft. and 1000 ft., and in general these plants do not ascend above to the Infer-Arctic Zone or descend below to the lowlands. They include Baneberry, Globe Flower, Wood Geranium, Bird Cherry, Rowan, Myrrh, Melancholy Thistle, Wood Club Rush, etc. Some are maritime plants, as Thrift, Sea Campion. The pseudo-montane group includes plants intermediate between the descending and ascending species, which may grow in the lowlands and on the uplands, as Bog Violet, Sundew, Grass of Parnassus, Cranberry, etc.
The ascending species are more lowland types, and they include general-ascending and sub-ascending species, the latter rarely ranging above 150 ft., and including few northern types, as Rest Harrow, Hare's Foot Trefoil, etc. Some, however, are found at higher altitudes, such as Oak-leaved Mountain Avens, Gentians, Sheep's Fescue, etc.
The habitats of plants that grow upon hills and dry pastures generally are less diverse than those which come under the other groups here dealt with. There is, however, up to the highest limits of cultivation, a certain diversity in wooded areas that counteracts the otherwise open character of the hillside, which is one of its most striking characteristics.
The type of habitat, apart from wooded areas dealt with in Section IV, is generally speaking pasture. It may be a calcareous pasture, as that favoured by Rock Rose, Hairy Violet, Silky Mountain Vetch, etc.; or it may be an upland neutral grass-land, where Dropwort, Field Scabious, etc, are found; or sandy, rather barren pasture, with Sheep's Sorrel, Sheep's Fescue, etc. The ground may be covered with rock fragments, with a shallow bare soil, and practically constitute a sandy heath, where Wild Thyme will grow.
Where the ground is largely waste upland Cotton Thistle will be found, and other plants of more or less casual origin, with ordinary pasture plants of the lowlands.
The wet hill pastures grade into moorlands, Cotton-Grass associations, or those made up of Sedges, Rushes, Grasses, and under favourable conditions Sphagnum bogs, etc. In ordinary wet upland pastures the Yellow Balsam and Gentians are found, with other hygrophilous or moisture-loving plants. These distinctions are important, as helping to determine the sequence of formations and the derivation of one from another.