Flowers that grow by the sea must cope with exposure to wind and salt spray. Those living on shingle beaches also have to adapt to shifting shingle and lack of nutrients; nevertheless, many species manage to flourish under these tough condition.
The number of multiple species of plants found on shingle foreshore is limited to about half a dozen species on any one beach. In fact it is more usual to find only two or three species. Surprisingly probably it is not a lack of fresh water that makes shingle foreshores such a difficult environment for flowering plants. The surface layers of shingle are actually well supplied with rain and dew, which provide a reservoir of fresh water that rests on the deeper salt water below. The pebbles seem able to hold this water on their surface and even in a drought the plants that live on shingle are green and fresh when inland plants may be wilted and brown. Nor does the salt spray or the exposure to wind pose any particular problem, for many plants living near the sea tolerate wind salt, yet cannot survive on a shingle foreshore.
Well, the real difficulty is the instability of the substrate; the constantly shifting pebbles damage any seeds and seedlings before they can grow large enough to withstand such movements. It is only after the beach has become stabilized above the high tide mark, where the sea does not cause constant movement that large scale colonization can begin.
Early colonists Lichens such as the black Verrucaria Maura and the yellow Xanthoria parietina are the first go appear, and gradually the spaces between the pebbles fill up with lichens, grit and shell fragments. A rudimentary soil begins to develop very slowly. But there is still one problem for colonizing plants lack of nutrients. Almost the only source of organic material, apart from dead lichens, is tidal drift. This explains why the spring high tide mark, with its line of dead seaweeds, driftwood and decaying skeletal remains, is one of the best places to look for the few flowering plants that can tolerate this harsh environment. Those that do grow here often have more than one adaptation to help them make the best of the conditions.
Creeping rootstocks, complete plant cover does not form on shingle foreshores instead, individual plants are dotted along the strand line and above the high water mark. Sea campion is one of the most widespread of such plants, growing along with sea sandwort where there is sand mixed with shingle. These are both prostrate and low growing species, pressed to the beach to avoid the worst effects of the wind. Their creeping rootstocks penetrate the shingle in all directions and anchor the plants firmly.
The sea campion forms spreading cushions of bluish leaves, and is covered with white flowers from May to July. Like many of the inhabitants of shingle beaches, it is not confined to this environment, but is rather an opportunist with an ability to survive in most maritime habitats. As a result it is not only found on shingle foreshores, but also on cliffs, sandy banks and at the edges of salt marshes all-round the British coastline. Norfolk and Anglesey, but it is now extinct in many of its southern localities. The root of this plant produces a multitude of white stolon’s (rooting creeping stems) which grow through the shingle to produce new plants each with several prostrate stems and large, blue green leaves.
Root adaptation shingle foreshore plants usually have long, tough, woody roots, well able to withstand the friction of the pebbles. Many of the species, like sea pea, sea beet and curled dock, have tap roots that delve deep into the shingle, anchoring the plant firmly while remaining within the freshwater layer. The sea pea is locally abundant on the shingle beaches of the south coast, including Chesil Bank. It is a perennial, prostrate species, bearing purple flowers from May to August. Like the non-maritime members of the pea family, its tap root carries nodules containing nitrogen fixing bacteria. Gardeners and farmers make use of this characteristics when plant clover in fields and lawns; when these leguminous plants die, they have the soil enriched with nitrogen.
In a nutrient poor environment like a shingle foreshore, this nitrogen fixing ability of the sea pea is especially valuable. Yet surprisingly, this does not seems to give the plant any great adventure and it is relatively rare, appearing only on shingle foreshores in the south and south east of England and north east Scotland. The sea beet, like the sea pea, is a rather straggling perennial. It is more common growing along the drift line on both shingle and sandy foreshores around most of Britain’s coastline. Its small green flowers appear in loose clusters from June to September.
The maritime variety of the curled dock has a tall flowering stem which is surprisingly sensitive to salt spray. In flower from June to August, it can be killed by a summer storm. It overwinters by retaining a rosette of dead leaves survive through the winter and in spring side shoots begin to grow to replace the dead aerial parts.
Sea kale has a large, fleshy rootstock that acts rather like a tap root. It is an unusual perennial plant, growing along the drift lines of shingle and sandy beaches around the coastline. It grows much larger than many of the other foreshore plants with larger, wavy, blue green leaves and dense heads of white flowers that appear from May to August.
Water retaining leaves, thick stalks and fleshy water retaining leaves are among the adaptations to life on the shingle foreshore. Shrubby sea blite is rather different from most of the other shingle species, being a 90cm tall shrub rather than an herbaceous plant. It has fleshy, water retaining branches and leaves which are blue green in color. The solitary greenish flowers appear in the axil of the leaves from July to October. It grows only where the drainage is very good, so a shingle foreshore suits it well, although it also grows on the e borders of sea marshes. The seeds of this species are distributed by the sea and they germinate on the strand line when they are washed up on the beach. Shrubby sea blite is locally common Chesil Bank and certain shingle beaches in Norfolk being the best places to see it.
Another shingle growing member of the same family, the Chenopodiacea, is the frosted sea oraches. This species takes it name from the frosted silvery appearance of reddish prostrate stems, fleshy leaves and greenish flowers. The flowers are unisexual, male and female appearing together on the same short spikes from July to September. Frosted sea-orache is an annual species, dying away in the autumn.