Science

Country diary: Heavy metal botany on the banks of the Tyne | Environment


This lowland pastoral landscape around Northumberland Wildlife Trust’s Close House Riverside reserve, on the north bank of the Tyne, is an unlikely place to find a mountain wild flower, the nationally scarce alpine pennycress. But in spring, an area of grassland about the size of a football pitch is enlivened by its blunt-ended white flower spikes, tinged mauve when they first open.

Percy Thrower, whose TV gardening shows earned him celebrity status in the 1960s and 70s, would surely have had a theory as to why this montane member of the cabbage family thrives here. He often prefaced answers to botanical conundrums with the phrase “the answer lies in the soil”, and that indeed explains why Noccaea caerulescens is abundant on the reserve. This is calaminarian grassland, a rare habitat contaminated with centuries of accumulated heavy metal deposits, washed downriver from mine spoil tips in the high Pennines – arguably one of the happier outcomes of pollution, for this species at least.

Alpine pennycress roots are comfortable here; it’s a metallophyte, safely accumulating zinc and lead at concentrations 30 times higher than would kill most plants. Its local abundance is the consequence of floods and an industry that began long ago, when people first learned to mine and smelt metallic ores.

That might also explain why we found a morel toadstool here, in riverside woodland a little further downstream. This gourmet’s delight, eagerly sought by fungal foragers in spring, has an affinity for heavy metals. Experiments in China, inoculating industrial sites with its mycelium, suggest that it could prove useful for removing toxic metal residues from contaminated land.

I’ve never tasted this uncommon, weirdly fascinating toadstool, with its tennis-ball-sized honeycomb cap. It resembles a brain on a stalk, so much so that it might be no surprise if it pulsated. Poisonous when raw, but an epicurean delight after cooking, apparently; morel with chicken breast, marsala and cream sounds tempting, though seasoning with unknown concentrations of toxic heavy metals makes it less appealing. I’m fascinated by fungi for their otherworldly beauty and biology, rather than their culinary potential – and this is a nature reserve, so harvesting it would be out of the question.





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