J Harbord Lewis
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.