Field penny-cress (Thlaspi arvense) is
found on wasteland throughout Great Britain, although it is a non-native
species. It is possible that the plant came into the country accidentally
alongside a consignment of crop seeds.
It
is an unwelcome weed when it invades farmland, especially as grazing animals
refuse to feed on it due to its unpleasant smell when crushed or bitten.
Field penny-cress has upright leafy stems,
sometimes with branches, that grow to a maximum height of 24 inches (60
centimetres) when flowers and then fruits are produced. The leaves are narrow,
toothed and stalkless, grasping the stem at their base.
The small white flowers appear from May to
July. They grow on stalks and in clusters. The fruit are what give the plant
its name, because they are almost circular and flat, with broad wings, albeit
with a notch at the top. The size of the fruits, at up to three-quarters of an
inch across, is not far short of that of a modern British penny, but it is very
much smaller than the pre-decimalisation pennies that were around when the
plant would have acquired its name. Curiously enough, the plant has a similar
name derivation in German, being the “feld pfennigkraut” – maybe the old
pfennig was closer in size than the old penny!
© John Welford
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