Purple gromwell is a rare plant of woodland areas found on limestone-based soils. It is limited to a small number of sites in Wales and South West England.
Purple gromwell is a short perennial with downy leaves. It has creeping, woody stems and spreads both through its seeds and by its stems rooting. The flowers are funnel shaped and at first are red, then as they open they become a deep purpley-blue.
As the flower develops, the acidity of the cell sap changes from acid to alkaline and the change in colour from red to blue occurs. If you want to see this colour change happen faster and in reverse, try putting a blue flower from a harebell or forget-me-not on a wood ant nest. As the wood ant's spray formic acid on the flower, small red patches will start to appear.
Like other members of the borage family, purple gromwell is attractive to a wide range of pollinating insects.