Toxin-tolerant plants take root in colliery's spoil tips

On a grey day in a tree-less landscape, buffeted by a bone-chilling north-easterly wind, only the calls of curlews and oystercatchers that had returned here to breed suggested this must be spring.

But when we reached the stony, undulating, ground near the entrance to the “governor and company’s level”, a mine tunnel driven into a hillside almost two centuries ago by the London Lead Company, we found an infallible floral indicator of the season.

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Every year the spoil tips around the mine entrance become rock gardens hosting the dainty white blooms of spring sandwort (Minuartia verna). Unwittingly, the miners who hauled ore out of the tunnel, leaving waste rock in heaps beside Middlehope burn, created a perfect habitat for this nationally scarce wild flower.

Few rare plant species can have benefited more from industrial pollution. Spring sandwort is a metallophyte, a plant with exceptional tolerance of soils contaminated with toxic heavy metals such as lead, zinc or copper. It can excrete the toxins through specialised pores in its leaves, which are then washed back into the soil by rain. It also stores high concentrations in its cell walls.

Meanwhile, the sea of less well-equipped moorland grasses surrounding these chemically inhospitable, barren, islands of shattered rock is kept at bay by lethal concentrations of minerals.

Further down the valley, on mossy turf near White’s level, we found ourselves taking pains not to step on the mountain pansy (Viola lutea), another lead-loving wildflower. This plant blooms in profusion here every spring, when the surrounding grasses begin to display a green haze of new growth. Its flowers hug the ground, raising their faces just high enough to attract the attention of the first insect pollinators.

Few sights do more to encourage the passerby to linger on a bleak day than these insouciant purple jewels in the turf.

By the time we reached Slitt wood, pausing to admire a single sentinel early purple orchid, we were as glad of the trees’ shelter as miners must have been on their way home to Westgate in the valley below. Soon we were surrounded by drifts of primroses and ramsons, more familiar signs of spring, under a canopy of newly unfurled foliage.