This grower is fairly sure of this plant identification.
Yellow loosestrife, Loosestrife
Lysimachia vulgaris (Yellow loosestrife). This perennial has creeping rhizomes with upright stems the leaves are broad green and grow in whorls of three or four. The flowers are star-shaped golden-yellow they are borne in loose terminal spikes in the summer.
They will prefer a slightly acidic soil with a good mix of organic matter, they need full sun or partial-shade. You can propagate from seeds or cuttings, or by division.
Suitable for the border or rock garden. Ground cover.
Italics = data drawn from parent genus or speciesView Full Plant Finder Record