It’s that time of year again when a lucky group of 1st year undergraduates from the University of Manchester head to the Mediterranean to learn about plant evolution and adaptations. This year in Mallorca we stopped at a slightly wetter part of the Albufereta, a small salt marsh near to the town of Alcudia (north-west of the lager famous wetland and Ramsar site, the Albufera). With more water in evidence, this part looked like a better place for the students to learn about mechanisms plants can use to tolerate salt stress.
The area is dominated by three plant species Arthocnemum macrostachyum (Glaucus glasswort), Halimione portulacoides (Sea purslane) and Juncus maritmus (Sea rush). Each of these has has specialised mechanisms for living in high salt, waterlogged soils such as succulent stems, the ability to exudes salt onto the leaves or air-filled spaces within the leaves and stems.
Patches of slightly higher ground, however, allowed other plants to grow, including this Grey birdsfoot trefoil (Lotus cytisoides). The weather had been a little cold over the preceding weeks and as this was one of the few plants in flower it was getting a lot of attention from the bees.
We see a lot of this plant on the strand-line and sand dune systems around Alucudia. It is clearly also salt-tolerant, but likes freer-draining soils and cannot cope with waterlogging. In flooded soils, air spaces fill up with water and bacteria rapidly use up available oxygen. Without special adaptations, plants in waterlogged soils can die as their roots are effectively suffocated as the flow of oxygen and carbon dioxide in and out of the roots is limited. Roots can then be invaded by fungi and other pathogens and the above ground parts of the plant suffer as water and nutrient transport from the roots is affected.
No-one enjoys traffic jams, that would be like looking forward to going to the dentist or hoping for higher taxes. Yet I found myself, earlier this week, supplicant before the great Gods of Traffic, asking for a jam… just a small one… in a particular place on the way to the University! Why this strangely aberrant behaviour? Well, this is a herbology blog and I wanted to get a close look at an unusual botanical success story.
In the warm spring sunshine it is easy to forget that three months ago Britain was in the grip of the coldest winter for more than a decade. Temperatures plummeted to -18 C in rural Cheshire, the University was closed for several days, and the landscape was blanketed in thick snow. Road salt was in heavy demand, and its use was concentrated on the motorways that the politicians insist oil the wheels of industry.
Three months later in the warm spring sunshine, swathes of starry white flowers have erupted along mile after mile of the M62 motorway. The story is repeated on many other motorways across the country. In some places there is almost a monoculture: white flowers stretch as far as the horizon.
The plant is Danish Scurvy Grass (Cochlearia danica), a saltmarsh species, which arrived in Britain in the Middle Ages. It is hardy and well adapted to hot, dry, and above all salty conditions. Danish Scurvy Grass flowers early in the year. It outcompetes native species in the roadside environment, where it tolerates the salt produced by gritting.
Most Scurvy Grass specimens in the herbarium collection date from the nineteenth century. They are from locations such as Hilbre Island in the Dee Estuary and show that the plant was restricted to salty coastal environments at the time. Their distribution now also mirrors the British motorway and trunk road network, taking advantage of a habitat that simply didn’t exist in the nineteenth century. This illustrates one of the many uses of herbaria, mapping the changing distributions of plant species… as described in a previous post.