Siberian Iris

Yesterday evening, a handful of us were taken to see this and several other blooms on a clump of plants growing wild in Fish Creek Park. The couple who generously led the way are keen to find out the ID of this species. They had been told that it might be an endangered species - or perhaps it is simply a garden escapee. They were definitely a "sight for sore eyes" : ) Any help with ID would be extremely welcome! The scientific name would also be much appreciated, as naturalists and botanists are involved with this, too : ) Later: thanks, Doug, for the confirmed ID of Siberian Iris!