Corydalis (cor IH dah liss) species produce ferny foliage on neat mounded plants and have numerous tubular blooms with small spurs that are produced in the spring, then intermittently thereafter, across the growing season.
Of the 300 species of biennials and perennials, the perennials are the ones that grow from tubers. They like full sun to part-shade and rich well-drained soil that is moisture retentive. They don't transplant well but do self sow.
Corydalis lutea (LOO tee ah) has blue/green-gray leaves and yellow flowers in zones 5 to 8.
In my zone 5 garden, they have self-sown in a rock wall and down cracks in the side of a set of cement stairs. The effect is lovely, and I could never have achieved such an abundant display intentionally. They just seem to know how to self-sow in exactly the right place!
When I try to transplant them, I have about a 30% success rate, though I've read that they can be transplanted in early spring and early fall.
One sees these fellows growing exuberantly in stone walls outside picturesque cottages in England. Recently I ordered a Corydalis with pinky-red flowers from a catalog. I do well with the yellow but have never been successful with the blue, so now I am hoping that the red one likes my yard and decides to relocate there.