Lysimachia paridiformis var stenophylla is an unusual Lysimachia growing best in moist soil in some shade and associates very well with Hellebores, ferns and other woodland plants. yolk-yellow flowers appear in late spring in dense clusters within parasols of deep green foliage.
It is low growing but bushy perennial.  30cm x 60cm. 
Remove old flowered growths. Rare.