It is probably a bee pod .A cross polination by a bee- the one with the pod and another iris.
The pod contains seeds.The seeds will not look like the iris the pod is on.
The pod has to turn brown and start to split open for the seeds to be any good to plant.It has to stay on the stalk until it begins to turn brown, not cut off.
It is up to you if you want to save the seed pod .Not all pods will have seeds in them.
It might take 3 years for the seeds to mature to bloom.
