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.
Sea Holly, Samphire, Absinth, Centaury, Sea Plantain, Sea Club Rush, Marram Grass, Crested Dog's Tail Grass, Seaside Manna Grass, Rushy Wheat Grass, Lyme Grass, and these continue in flower till August and September. Not until August do Sea Campion, Sea Rush, and Grass Wrack commence to flower.
There are several reasons why maritime plants should be uniform in their duration. They flower late as a whole, hence there is scarcely scope for many of an annual or biennial nature. The depth to which their rhizomes and roots penetrate demands that they should be of long duration, for such a foothold must be obtained before the necessary flowering and seeding can occur, and this takes a long time to secure.
The possibility of germination is rather remote, for there are so many disadvantages with which the seeds have to contend, even if they are not blown completely away from their suitable habitat (as may happen in a large number of cases). This causes the small patches of many species. Hence it is not surprising that maritime plants are almost entirely of a perennial character. The great development of the vegetative parts of such trailers as Sea Campion, etc., and their resting buds or hibernacula, are all characteristic of perennials.
A few, however, are annuals, producing much seed, as Yellow Horned Poppy, which, sometimes, may be also perennial. Sea Rocket, a fleshy plant, is also annual, and so again are Saltwort, Crested Dog's Tail Grass, and Squirrel Tail Grass. Scurvy Grass and Woad are biennials. All the rest are perennials, herbaceous, and deciduous, and except two shrubs die down in winter as a rule.
As one walks along the shore one is struck by the almost entire absence of land animals. All the forms one meets with are in fact marine animals, and these are the flotsam and jetsam of the waves, save in the little pools left by the tide where some living shells, starfish perchance, or sea urchins, manage to survive. Rocky coasts are more prolific. But the most obvious factor to the entomologist is the absence of insects. This applies to the low sandystretches. Chalk cliffs and other rocky coasts with land plants, such as heaths, etc, are, however, very often the habitat of butterflies. Beetles are the most frequent insects on the coast, and a few species are known to inhabit the salt water itself.
These facts have a considerable bearing upon the pollination of plants along the shores. For in the absence of insect visitors plants adapted for cross-pollination by insects are unable to effect cross-pollination. It, however, self-pollination is also possible seed will be set. Sea Campion is proterandrous whilst Sea Rush is proterogynous, two examples showing that there is a tendency to promote crossing. Sea Lavender is dimorphic. Several sea-coast plants are pollinated by aid of the wind, as Absinth, Sea Plantain, Saltwort, Sea Club Rush, and the grasses Crested Dog's Tail, Seaside Manna Grass, Rushy Wheat Grass, Squirrel Tail Grass, Lyme Grass are also pollinated by the wind. Grass Wrack is pollinated by water.