Gets it's name from the growth habit. It flowers and the flower heavily droops to the ground, then a new plant forms as it sits on the ground. And, on and on...
The beautiful Japanese Iris "Gamecock" with more blooms...
And, the one that saved my life-- Iris pseudocorus "Yellow Flag"
An Iris dealer I would recommend:
Ten Easy Rules to Follow for Beautiful Blooms:
Let me know if you can't read this and if you should want it, I'll send you a copy.