What causes this?

This is a new bloom stalk (reblooming) on what is supposed to be 'Immortality'.
The stalks begin horizontally then turn vertical, much as in bowl shape. Both
first bloom and rebloom tend to be the same. I did cut the leaves back after
first bloom to expose the rhizomes to sunlight to clear up some spotting problems.

I may have 'Immortality' confused with 'Lo Ho Silver'. I think LHS is a smaller
plant. I purchased both at the same time--pity the fool who doesn't keep tags.

Forgot the pic.

Lo Ho Silver is an IB so shorter. Has a neighbor been using roundup which might have blown into your garden? If not it could be weather related. A friend in England had distorted stalks when a neighbor to her alottment used roundup in his.

Ocassionally I have this issue with established clumps, it is usually from climate change or alot of rain. Don't fret, it will be fine.

IrisMA--I think you nailed it. I rechecked the original catalog page and
'Lo Ho Silver' was sold as an intermediate, multiple rebloomer. This is
the one I had thought was 'Immortality'. It has always bloomed first of
all before the other TB's, about the same time as the old antique whites
I had dug on a former employer's property. It tried to rebloom last year
in early November but was frosted. The fans have a tendency to flatten
out away from the center which would account for the directional growth
of the stalk. It does form a bowl shape with the stems and is not as
high as the typical TB. It is beautiful and a possible triple rebloomer
and I would recommend it to anyone needing a shorter white iris.

There is a plant by the same hybridizer (Monte Byers, now deceased) named High Ho Silver which is a regular TB. The IB is more popular as there are more reblooming TBs.

First rebloom after the leaves were cut back in June because of leaf spotting.

Update: Closeup

overview

New stalks--3 forming

stalk size. verifies probably LHS intermediate. Excellent rebloom.

glad that the conditions improved & you had rebloom.