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.
The surface of the country, once perfectly level, has become extremely diversified, owing to various causes, such as disturbance of the crust, denudation and river development.
We therefore find that meadows may be lowland or upland in character. The lowlands are characterized by such well-known plants as Meadow Sweet, Great Hairy Willow Herb, etc., whilst upon the uplands grow Dropwort, Lady's Mantle, and many others. As a rule, the plants of the lowland meadows are allied to the marsh plants, and have come to us from the north with the Great Ice Age, or previously, whilst the upland plants are, though at the highest altitude palaearctic types, usually of southern origin.
The vegetation of the upland meadows has an affinity to the vegetation of a hill, but in the last case the flora may be much less disturbed and influenced by cultivation, and in this way the floras are distinct. Altitude can thus be shown to cause great differences in a flora.