Halophytes on the move along our roadsides

July 13th 2019

Driving along Assynt’s roads in early summer, you may notice the occasional patch of rich yellow flowers right at the edge of the tarmac (photo 1).  A carefully chosen stop reveals that these arise from a carpet of silvery pinnately-divided leaves (photo 2).  This is silverweed Potentilla anserina, a close cousin of tormentil P. erecta, whose smaller, four-petalled yellow flowers star our heathland.

One of the original habitats of silverweed, where it may still be found locally, is along the upper edge of sandy and shingly seashores, evidence of its ability to tolerate salt.  This tolerance has enabled it to colonise the margins of our winter-salted roads, together with a number of other halophytes (salt-plants) originating on our coasts.

Conspicuous amongst these is sea plantain Plantago maritima, whose tight rosettes of angled succulent leaves can form continuous bands along roadsides.  They bear elegant narrow spikes of yellow-stamened flowers (photo 3).  In late summer, sea plantain can turn a curious pinky-purple colour, due to wholesale infection by a powdery mildew Golovinomyces sordidus.

Other roadside halophytes frequently found in Assynt include the pink-petalled lesser sea-spurrey Spergularia marina, which is now much more often found in this habitat than on seashores.  The tiny sea pearlwort Sagina maritima eluded us during fieldwork for the Flora of Assynt, but we found it on a roadside at Knockan on 27th July 2013 and, having got our eye in, we managed to locate it on the coast at Achmelvich the same day.

The same roadside at Knockan yielded, on the same day, our first local sighting for reflexed saltmarsh-grass Puccinellia distans ssp. distans. This former denizen of saltmarshes has become a spectacular invader of salted roadsides in England since the 1970s, and from our current experience is now on the move in the north of Scotland.

Our often busy roadsides have to be botanised with care, but they are proving a profitable source of ‘new’ discoveries.

Ian Evans

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