Macleaya cordata
Has received the RHS Award of Garden Merit. (1993)
The Plume poppy is a striking architectural plant, with tall upright stems and attractive grey to olive-green, lacy foliage. In summer, the stems are topped by long airy sprays of buff white flowers. Plants are slow to get going and often barely grow in their first season but, once established, they can spread quite rapidly. If space permits, plants look best when allowed to develop freely into large clumps, especially when used as a feature in the same way as pampas grass. [BBC plant finder]