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

Wylam, Northumberland: Why would a rare mountain flower be found here? The answer lies in the soil

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.