A clump of contrasting foliage within a mixed border is always welcome. A border full of Lysimachia ciliata is a different matter.
This North American native has an invasive root system that results in pervasive invasion. May is the time of exponential growth, get your border fork and prepare to do battle with this bronze foliaged, yellow flowered border coloniser. As well as colonising rhizomes the root mass is made up of masses of white fibrous root with the ability to extract soil moisture to the detriment of other plants.