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 factors of the maritime habitats cause the plants in each zone to have marked characteristics. Generally the sandy coast vegetation is composed of fleshy herbaceous types having a branched or pyramidal habit. In many cases the upright erect habit, giving the plants a strict appearance, is developed. Others are trailers, as some Oraches, Sea Bindweed, Sea Purslane, etc., and Sea Heath is a shrubby type of trailer. Some are rosette plants, as Thrift, Buckshorn Plantain (and these are most general on rocky coasts). The grass habit is adopted by a few, as Centaury, Woad, and the number of Sedges and Grasses is large. A few are shrubs, as Sea Buckthorn, Tamarisk (the latter with ericaceous habit), Coto-neaster, the first spinose.
On the shingle the habit is trailing, and the plants produce resting shoots or hibernacula, as in Sea Purslane, Sea Campion (procumbent). A few are pyramidal, and all are fleshy, with the Sea Kale type of habit, as in Sea Holly, Yellow Horned Poppy, etc.
On the dunes the habit is trailing, as in Seaside Bindweed, with subterranean stolons, and the grasses produce long rhizomes, deeply rooting. The grass habit is the dominant one. In the salt marshes the habit is largely the grass habit of the rushes, sedges, and grasses. The shrub type is represented by Sea Blite. A few have the rosette habit, as in Sea Lavender, Thrift, Buckshorn Plantain. The trailing habit is adopted by Sandwort, Sea Milkwort, Procumbent Sea Blite. Arrowgrass and Sea Plantain also have a grasslike habit. The bulk of the plants are fleshy, except the grasses, etc., and the shrubby types. Samphire has a very marked strict habit.
Most of the maritime plants are herbaceous perennials. Only a few attain the size of shrubs, and these are quite local. Trees as a whole are absent. The factors which regulate the height of maritime plants are chiefly wind, and the various ways in which they are subjected to exposure. The manner in which the few trees that grow by the sea-coast are affected by wind and dwarfed has been shown. The shrubs, as Tamarisk and Sea Buckthorn, are affected in much the same way. Many of the plants, especially those that grow next to the sea in the first or second zone, are trailing or procumbent plants, as Sea Bindweed, Sea Purslane, Sea Campion, etc.
The succulent character of so many of the maritime plants prevents them from attaining any great height, apart from the foregoing factors. Their increase by growth is thus lateral, not upward. The softness or looseness of the soil also favours a low shrubby habit, even amongst those that are more diffuse, as in the case of Yellow Horned Poppy and Sea Kale. Plants with the erect habit frequently also have a procumbent habit in some situations, and there are some plants again, of which there are several species, in which one is erect and others are procumbent, showing that the latter is of advantage to the plant, and an adaptation to maritime conditions. Of such type are Shrubby Sea Blite, which has an allied species, Procumbent Sea Blite, and Samphire, of which there are numerous species (recently defined by Dr. C. E. Moss), in which all stages from the erect to the prostrate habit are represented. These facts tend to show that the height of maritime plants is generally low, since a low height is most favourable in such habitats.