Hylomecon japonica is a small perennial woodland poppy relative from, naturally, Japan. It is not often found in gardens (at least that I have seen), and its bloom season is brief, but it is lovely. It doesn't take up much room and the foliage disappears sometime during the summer, so it is not any real trouble to have around, and is well worth the small space it takes up. It sets rather few seeds, maybe more than one clone would increase seed set? Or maybe it is a function of the weather during its bloom period in a particular year. It grows well with other woodland ephemerals such as the Trillium grandiflorum (visible in the lower right corner of one of the photos) and hepaticas. I got my plant some years ago from Oliver's nursery in CT, and it is available from a few mailorder nurseries, especially those that cater to rock gardens.