Salty tales of Strand-line Plants

These are three different species that we saw recently in Northumberland which belong to a select group plants that colonise the strandline on the seashore. They live in that narrow zone just above the extreme high water mark, usually marked by a line of dry seaweed. It is hard to imagine a more demanding environment; it's dry, salty, and often hot and windy, so the plants are often blasted by wind-blown sand.

This is sea rocket Cakile maritima, the most attractive of the three strandline specialists that we found.  It's a member of the cabbage family and is an annual species, germinating in spring and quickly putting down deep roots into damp sand below the surface.

Sea rocket seed pods are corky and water resistant, acting like lifeboats that can carry seeds long distances in safety on ocean currents. A species of sea rocket was the first higher plant to appear on the volcanic island of Surtsey in 1965, just two years after the island appeared above the waves.

Sea rocket's mauve flowers are attractive to bees and cabbage white butterflies. 

Dealing with salt in the moisture around it's roots is a challenge and it manages this by sequestering the salt in vacuoles in its succulent leaves.

Frosted orache Atriplex laciniata, another annual, has a different way of dealing with the salt, by pumping it into glands on the leaf surface.

It forms extensive stands along the strandline and ......

... the leaves develop this grey appearance.

This is due to a coating of swollen hairs, seen here under the microscope, where salty water accumulates and then crystalises.

The dense covering of salt-laden hairs is highly reflective and as they die that either fall off or are washed away by rain, ridding the plant of toxic salt.

In this vertical section through an Atriplex leaf, magnified under the microscope, you can see the swollen hairs on both sides of the leaf surface, separated by the green photosynthetic tissue of the leaf itself.

Finally this is prickly saltwort Salsola kali, a tough annual that could ruin your picnic if you happen to sit on it because the leaf tips carry short but sharp spines. The minute white flowers are carried in the axils of the upper leaves.

Here the plant is growing just above the strand line below Alnmouth dunes.

These plants show another hazard that these strandline plants face - constant burial by trapped particles of wind-blown sand. Maybe that's why the flowers are produced at the shoot tips.