Autumn Damask mutated cane

Autumn Damask has been a healthy newcomer in my garden, ordered bare root from a reknowned French nursery/hybridizer early this year.
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After her first flush in May I deadheaded her and she has been growing fine, except for a cane in the center that was a little slow and had a slightly bluer tinge to the foliage, but I didn’t think much about it.
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Today I was deadheading her neighbor Darlow’s Enigma when I noticed something white. At first I thought it was a petal from DE. Upon closer inspection it was not.
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I am including more pictures below.
This is really weird looking. Half petal, half leaf? Anyone know what causes this?

More pics of that petal/leaf:
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The reverse:
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Full cane with more distorted leaves above the petal/leaf… I wonder what that terminal bloom will look like.
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The closest I’ve seen to your leaf/petal is a leaf/petal on a tulip.

But I did see some sepals on ‘Marquise Boccella’ transformed into leaves.

O. F. Cook (1926) described these interesting oddities as Metaphanic Variations:
http://bulbnrose.x10.mx/Heredity/Cook/Cook_Metaphanic/metaphan.htm

Thank you very much for that information and the link to the article, Karl K!
Metaphanic Variation… That’s a term I’d never heard before. Very interesting! Fascinating to read Cook’s discussion about variation and evolution too.
I had come across a couple pictures of tulips doing this online when I had googled “half leaf half petal”. It seems to be (somewhat) more prevalent in tulips.
Near the flowerbud, things continue to be weird, and it looks like there will be more “metaphanic variations” happening there too.
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Out of curiosity, I took a flashlight to the back of the weirdo to see if it was veined like a leaf. It seems to have just a beginning of a central vein or at least a slightly thicker central line, that doesn’t branch off.
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You see this kind of growth where petals form from stamen in rose flowers and petals and stigma fuse and morph in double hibscus sinensis blooms.