Moor Green Lakes Group
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Himalayan balsam Impatiens glandulifera is a relative of the busy Lizzie, and has become a major invasive weed problem particularly along soft damp ground such as river banks and ditches. They are efficient colonisers, when the seeds ripen, they explode and can be ejected several feet from the mother plant. As a consequence the plants can quickly take over an area, reducing biodiversity and causing erosion.
The RHS has some good information on the plant here.
Images from Wikipedia