Although Macleaya cordata is know as Plume (or Plumed) Poppy, I always thought it was just a name, not really a realtive. There are plenty of plants like that. After all, it didn't really look like a poppy in flower, leaf or size. This is a big guy, usually ranging from 6-8 feet tall. It spreads by stolons like the Eomecon from yesterday, but this one seems to be difficult to transplant (and doesn't spread nearly as far or fast as the Eomecon). The leaves are large, greyish-green above and a paler greyish-white underneath. The leaf veins are quite prominent. Its tiny flowers are borne in large feathery panicles. I don't think they are especially good as cut flowers, though I've never tried. This family isn't know for being good for cut flowers unless one cauterizes the stems immediately upon cutting the blooms with a match or lighter.
Macleaya cordata is a native of eastern China and Japan, where it is a plant of the woodlands, gullies and scrublands, generally in the mountains. It flowers in June and July, though the flower plumes persist for quite some time after that. The flowers are so tiny that unless you're really close (and unless you're tall, you won't be really close to the blooms) you won't really be able to tell the difference between fresh and older blossoms. It was introduced into cultivation in 1795 as Bocconia cordata, an incorrect name by which you still sometimes find it, and the name under which I first obtained it.
There is one form 'Flamingo' in cultivation, though I don't grow it here. It has pink flushed leaves and the flowers are also pink rather than the creamy color of the species.
In my garden, this is a plant of the shadier places. Being so tall, it makes a statement, even from the back of the bed. Quite a pretty statement, I think. I have it planted in one bed with among small trees and shrubs with bleeding heart, and the leaf colors are very similar to the Dicentra. In another spot, it grows mostly alone, under trees with only some hostas for companions.