Northern yellow-cress (Rorippa islandica) is found
throughout the British Isles, particularly on the edges of ponds and
watercourses and in water meadows. It can withstand having its roots immersed
in water during the winter but drying out in summer. It is sometimes
encountered as a garden weed.
The plant grows erect to about 24 inches (60 centimetres)
high, having a hollow stem. The leaves, which are deeply lobed, grow on stalks
towards the base but without stalks higher up. The stalks half-clasp the main
stem at their base.
The flowers, which appear from June to September, are small
and yellow, being visited by small insects such as flies and hoverflies. The
sepals and petals are the same length.
As the flower-stems grow higher, small oblong seed pods form
in clusters below them, each seed pod being held on a stalk that is about the
same length as the pod.
Northern yellow-cress is also known as Iceland watercress,
but it is not an edible plant like its relatives, the white-flowered
watercresses. There are several other varieties of yellow-cress that are found
in Great Britain (e.g. creeping and greater) and these are also inedible.
© John Welford
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