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 special character of the maritime habitats of plants naturally affects dispersal of seeds of plants. One feature to be noticed is the "spot-bound" character of many of them. Many species of seaside plants are restricted to a few localities. In other cases they are confined to small patches, perhaps owing to the character of the soil. The dominant types, however, as the Grasses on the sand dunes, locally form continuous associations. The less dominant types are in such cases discontinuous or sporadic.
In the salt marshes a number of the species form again extensive societies, or even associations, the conditions being more uniform. The seeds of maritime plants are, as might be expected where wind plays so great a part, largely carried by the wind. The following are dispersed by this agency, viz.: Woad (partly), Sea Campion (censer fruit), Tamarisk, Sea Holly, Samphire, Absinth (pollinated by the same agency), Sea Lavender, Thrift (parachute arrangement), Sea Plantain, Saltwort, and the Grasses.
The Yellow Horned Poppy disperses its seeds by aid of the tension in the pod, which causes the pod to split open and to jerk the seeds, which are numerous, to a distance. Other plants, as Scurvy Grass, Woad (partly), Sea Kale, Sea Rocket, Sea Purslane, Centaury, Seaside Bindweed, Sea Rush, Sea Club Rush, Sand Sedge, and Marram have also devices of their own for dispersal of their fruits and seeds. In Sea Buckthorn the berries are dispersed by birds. Grass Wrack is dispersed by aid of the water.
The outstanding feature of maritime vegetation is the saline character of the soil. Probably the area to which the land is subjected to spray from sea breezes is the limit of the area in which the soil is saline. Rocky coasts and those fringed by sand dunes may in a measure be less subjected to impregnation with salts from the sea.
Since the soil along the coast is largely sandy, it is quite natural that the maritime plants for the most part are equally at home upon sand soil without salt. Experiments made by the author with plants from each zone show that all of them can subsist inland in river silt without salt. The Yellow Horned Poppy, for instance, will grow and produce abundant flowers and seed in an ordinary gravel drive, and Sea Campion is if anything more luxuriant in river alluvium. Sea Heath does well under the same conditions. At the same time the xerophytic characters evoked by the excess of salt are largely lost when these plants are grown inland.
The zonation of the maritime plants and the diversity of the vegetation necessitates to some extent a different method of survey of each zone. But generally the method of studying meadow or pasture plants may be applied here, more especially in regard to the salt marsh, in so far as the mapping of the association is concerned.
The problems of soil character, origin of each formation, and its inception and growth, which are rather the work of the advanced student, need not be detailed here fully (see Professor Oliver's work on Blakeney).
In the case of the sandy coast, and the muddy coast, it is important to consider the continuous or discontinuous character of the plants that one notices. The distance of each from the sea at high tide, the zonation of each type within the first zone, the slope of the shore, and the aspect are each objects for study. The adaptations of the plants to the halophytic conditions are also points for observation. The shingle beach may be studied in the same way. On the sand dunes the part played by the Marram, Lyme Grass, and other Grasses in protecting the sand from erosion, and the influence of the Grasses upon the other types, will be the principal features to be studied. In the salt marsh the associations should be studied with a view to discovering the effect of one type upon another, and the order of colonization of each plant.