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.
A common characteristic of both bog and marsh plants is the moist nature of the habitat. The flora of a bog is exposed to wind and insolation, and sunshine for long periods, and it shows adaptation to these conditions. Little shade is afforded for the bog plants, except by the few shrubby types for the smaller plants, e.g. trailers.
The bog or fen vegetation may be extensive, and afford habitats for a number of different plants; or consist of a few plants, as Cotton Grass, making up a wide association.
Trees and scrub are much more frequent in a marsh than in an upland bog, and the marsh flora in any case exhibits a greater diversity as it merges into aquatic vegetation, which is very diversified.