Valeriana officinalis, a prolific seeder which is possibly why the geographical range is Eurasia. If you grow this herbaceous perennial you are in good company, found in the border by the pond but also selected by Gertrude Jekyll, (1843 – 1932), a lady who described herself as a working amateur. She created around 400 gardens having an appreciation of natural and formal design.
Do make sure you are quick with the secateurs to remove the flowered stems immediately the flower colour has gone. Conversely you may wish the natural garden look as Jekyll appreciated. Bare soil will rapidly become colonised with self sown seedlings. This is a tall growing plant, reaching two metres at flowering, so does have the propensity to take over an area rapidly.
Slightly scented, light pink / purple flowers populate the terminal inflorescence. The stems are ribbed longitudinally, linear red and a shiny green between.
Anyone who cultivates this plant will be aware of the unusual smell given off by the roots when handled. It does tend to linger even after a good handwash.