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 title of this section may seem paradoxical compared with the last. But whilst the conditions of vegetation are limited to certain types, the types met with upon the sea-coast are sufficiently diverse or composite. Thus there are sandy tracts of sea-coast, and others that are muddy. There are the mouths of estuaries, and alluvial flats or warp. There are again stretches of shingle with peculiarities of their own. Where rocks bound the sea-margin there are diverse types of soil derived from each type of rock. There are the special types of sand-dune, usually mobile, unless well stabilized by dune plants, such as Lyme Grass or Dwarf Willow, as in Anglesey.
There are again open or closed bays with brackish water in which Grass Wrack, Naias, and Ruppia grow, with characteristic brackish-water Algae and Mollusca. The salt marshes finally form another type, and one with very marked characteristics. In addition to these genuine maritime plant-formations there is a large flora of alien plants which have established themselves along the coast, on kitchen middens or elsewhere. The neighbourhood of docks and ports is particularly favourable, especially where grain is imported, for the introduction and establishment of such plants. The inland flora again is always encroaching upon the coast flora. So that taken as a whole, though the alien plants and those found near docks and ports rightly belong to other sections, the flora is decidedly composite.
The plants that grow by the sea-coast, also called strand plants, are distinguished from the inland types. The latter are adapted to a moderate supply of moisture, and are known as mesophytes, as meadow plants. They also differ from those that are adapted to dry summer conditions and cold or wet winter conditions, or tropophytes, such as deciduous trees, etc. Strand plants are in fact especially adapted to dry conditions. The same applies to the dunes and salt marshes as to the sandy sea-coast. This is due to the fact that in absorbing water, coastal plants would necessarily absorb a large proportion of salt, and since this would upset the balance of nutritive materials, the plant therefore takes up less water than it otherwise would do.
To compensate for this, the plant has a reduced leaf surface, few of the plants, except Yellow Horned Poppy, Sea Kale, and some few others, developing broad leaves. Most are linear or narrow and oblong. They are also, as a rule, fleshy and thick and succulent, e.g. Samphire, Oraches, Sea Holly,
The stems are equally fleshy and succulent. The herbaceous types, as Sea Blite, Sea Heath, have heath-like, small, short, linear leaves. The majority of the maritime plants are dwarf, and not luxuriant, and many are procumbent or trailing. Other factors are the thick cuticle or epidermis preventing ready transpiration.
The stomata are also sunk in this thick cuticle, assisting the plant in fitting itself to physiological drought.
The sandy and shingly character of the sea-coast, and the wind, cause the substratum on which they grow to be destitute of moisture, and the plants have largely to rely on atmospheric moisture.