Thanks, All.
Corydalis lutea spreads around here, but it's a gentle seeder.
The big thing for me is that it grows from a shallow fleshy root and not a corm (latter, e.g. C. solida).
Means it's easy to pull out, even rake away, where it's not wanted.
As others have said, it's got to take our prize for the longest blooming perennial (just about the whole growing season).
