These are just darling and a US NATIVE! It is native to the eastern US, as well as Washington, Oregon, Idaho and another handful of states.  Dutchman's breeches are a member of the bleeding heart family, which makes sense as that is what they reminded me of, with their delicate blooms dangling out on a long fishing rod-like stem, except instead of dangling hearts, they are dangling pantaloons! Ha! They are named such due to their appearance being similar to the breeches of dutchmen. 
 
Spring, Summer and even early Fall, depending on your climate, are the best time to plant these, as they need 12 weeks of warm weather, followed by 12 weeks of cold weather for germination the following spring. 
 
Seeds are kept in cold storage and should remain in cold storage until they are ready to be planted
 
Perennial zones 3-7
 
This is for 20 seeds