A RASH of giant stinging nettles is breaking out over England, claim
botanists. The weeds which once skulked around the edges of meadows and in
graveyards are now sweeping across wide tracts of countryside and choking
riverbanks. The nettle thrives on phosphates in farm fertilisers and sewage
effluent in rivers.
A survey by the Wiltshire Botanical Society reveals that, in the past 40
years the nettle has become the most widespread flowering plant in the county.
Urtica dioica is 鈥渞ampant on canal and river banks; by roads, tracks and field
edges; in hedges and ditches; on dumps and waste sites; throughout many
pastures; in woods, copses, even downland,鈥� says local botanist Jack
Oliver.
It has 鈥渟queezed out much of the wayside flora in increasingly large areas
of England in the past 30 years,鈥� says Oliver. Growing up to 3 metres high,
the stinging nettle鈥檚 closely packed stems and large leaves deprive other
plants of the light they need, including the now rare stingless nettle, Urtica
galeopsifolia.
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The survey found nettle patches covering whole fields, and growing in
鈥渄ense, uninterrupted ribbons鈥� along the banks of phosphate-ridden rivers such
as the Avon and the Kennet 鈥� one of the country鈥檚 most important chalk
streams.
鈥淚t can be hard to find river sites without nettles,鈥� says Oliver. In the
last survey of Wiltshire鈥檚 flora, in 1957, stinging nettles did not feature in
the top 30 plants growing in any of the waterside sites.
Mike Grant, a botanist from Birmingham likens the outbreaks of nettles
along riverbanks to algal blooms in the water.
Historically, stinging nettles have been confined largely to field edges
and patches of ground rich in phosphates, such as graveyards, where rotting
bones provided a constant supply of phosphate fertiliser. But modern intensive
agriculture and discharges of sewage effluent have spread phosphates much more
widely.
Oliver believes that the stinging nettle could be adapting to take
advantage of the abundant supply of nutrients, extending its underground
networks of rhizomes during the winter, before bursting forth in ever larger
patches each summer. In the space of one winter a single plant can transform
itself into a nettle bed with a thousand stems.
English Nature, the government鈥檚 conservation agency, confirmed the
Wiltshire finding. 鈥淲e believe phosphates are a major threat to the biology of
many English rivers,鈥� says a spokesman. 鈥淧hosphate favours fast-growing plants
such as nettles and coarse grasses to the detriment of wild flowers.鈥� River
plants at risk include the white water-lily and floating club-rush.
The agency says that phosphates are a problem in 20 of the 25 rivers it is
designating as sites of special scientific interest. It has asked water
companies to remove phosphates from effluents discharged by 35 sewage works
into SSSI rivers.
Unfortunately for those stung by proliferating nettles, among the plants
disappearing beneath its shade is the dock, Rumex obtusifolius, the leaves of
which have provided countless generations with relief from the stingers鈥�
sting.