I planted some irises given to me by a friend last year. They bloomed beautifully! The one I am referring to is "Hello Darkness" It is a deep eggplant shade of purple it is almost black. This year it sent up one very thick and shorter stalk and the blooms on it do not even look remotely like the same plant! They are very short purple petals that are so stiff they seem almost plastic and very small. Can anyone tell me what would cause this??

Thank you!