Romneya are suckering subshrubs with pinnately lobed leaves and large white flowers in summer.
R. coulteri is a vigorous, suckering herbaceous perennial to 2m in height, with divided, grey-green leaves and poppy-like flowers 15cm in width, with crinkled, pure white petals and a boss of deep yellow stamens.
Grow against a warm, sunny wall protected from cold winds. Mulch deeply prior to winter. They dislike transplanting but once established it can spread, so site with care.